Swapped out the PSU with a known working one, upon plugging in the pwr cable, the pwr button back-lit GREEN and there were no longer any numeric codes blinking. Initiated a boot cycle but INTO Setup, confirmed drives are showing up, memory as well. Booted again, F12, into on-board diags, and everything passes the quick test. Might suggest the blinking 1 & 3 could have been residual effect from the failed PSU to begin with. Looks like blinking Amber pwr button supersedes the diagnostic numeric codes, at least until you remedy the power supply unit. Answer from Towster on dell.com
Dell
dell.com › dell community › desktops › optiplex desktops
Diagnostic leds 1 2 4 and then 3 ---> front power button failure ?!? | DELL Technologies
December 21, 2023 - On a Dell OptiPlex 790 the diagnostic leds 1 2 4 turned on, followed by led 3 only (while the power button was solid blue). Looking into the user manual, there is no such pattern or sequence of patterns, however, there is a led 3 only explanation of "A possible system board failure has occurred" with no light on the power button.
Dell
dell.com › dell community › desktops › optiplex desktops
Optiplex 960 MT blank screen...Diagostic LEDS= 1 2 3 and two beeps | DELL Technologies
December 8, 2022 - I really appreciate the help I get here on this forum, and I'm sure I'll be back. ... 1,2,3 with an amber power light is a failed CMOS battery, That would be a CR2032 which can be bought at a dollar store and is very inexpensive.
Dell Optiplex 780 power button blinking amber and 1 and 3 numbers blinking green
I have Dell optiplex 780 Mini Tower as my PC. The problem is the power button blinking amber and 1 and 3 numbers blinking green for about 2 minutes on startup then the system start normally and the... More on dell.com
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July 22, 2019Optiplex 745 will not boot: two beeps and 1-2-3 lights on
Hi all, I pulled out my old Dell Optiplex 745 to try and put it to some use and am having some trouble getting it to boot up. At post, the system will give two short beeps and display lights 1-2-3 solid green, 4 is off. Video does not display. I have tried many different things: 1. Stripping... More on forums.tomshardware.com
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October 21, 2012Dell optiplex 790 lights 1 & 3
lights 1 and 3 are indeed a ram problem. Assuming you didn't add new ram: - check for debris or dirt in the ram slots - try to put only one pair of similar ram. More on reddit.com
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July 5, 2020Dell Precision T3500 Diagnostic Lights 123 and 2 short beeps
The same situation happened here. It worked, then I added a 2GB stick of RAM to the RAM I had. It showed me an error about changing memory configuration. I pressed continue, and it shut down. So, I pulled the extra stick out, and now when it's booting, it goes like 3, 4 then 1, 2, and then 1, 3, 4. More on reddit.com
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July 13, 2023Videos
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If you get error codes 1 and 3 - this means you need to replace ...
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Dell
dell.com › support › kbdoc › en-us › 000153002 › a-reference-guide-to-the-precision-workstation-diagnostic-indicators
A Reference Guide to the Precision Workstation Diagnostic Indicators | Dell US
Dell Precision desktops have a long history of integrated diagnostic indicators. These can be audible beeps and specific diagnostics LEDs to indicate when during the Power On Self-Test (POST) a device is having issues. These models had a block of 1, 2, 3, 4, LEDs on the front of the chassis that either lit up Green or were off.
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Swapped out the PSU with a known working one, upon plugging in the pwr cable, the pwr button back-lit GREEN and there were no longer any numeric codes blinking. Initiated a boot cycle but INTO Setup, confirmed drives are showing up, memory as well. Booted again, F12, into on-board diags, and everything passes the quick test. Might suggest the blinking 1 & 3 could have been residual effect from the failed PSU to begin with. Looks like blinking Amber pwr button supersedes the diagnostic numeric codes, at least until you remedy the power supply unit.
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Dell Diagnostic Indicators According to the diagnostic indicators, lights 1 & 3 indicate a RAM problem. Blinking orange power light indicates a failing or failed PSU. I had a RAM problem with my 755 last year. Lights 1 & 3 lit up and power button light was a steady orange. How's the CMOS battery? A low battery can cause all sorts of bizarre problems. Replacement to rule it out is cheap. I'd try reseating RAM chips one at time, starting with no RAM. See if the error repeats. Remember to unplug power cord in between reaseating chips. If the error remains unchanged, I'd have to suspect the PSU. One of our other Rockstars or experts might chime in too. The light combo you had I don't believe is normally one seen together. You may also use the 'Get Help Now' option at the bottom right to chat with a Dell technician right away.
JustAnswer
justanswer.com › computer › moage-power-button-2-3-buttons-blinking-dell-desktop.html
Expert Solutions for Dell Diagnostic Lights and Blinking Codes
First, check the power supply unit (PSU) connections and ensure stable power input. Inspect RAM modules by reseating or testing them individually, as faulty memory often triggers LED codes.
Tom's Hardware Forum
forums.tomshardware.com › home › cpus
Optiplex 745 will not boot: two beeps and 1-2-3 lights on | Tom's Hardware Forum
October 21, 2012 - This pattern also displays when you enter system setup (see Entering System Setup) and may not indicate a problem. Ensure that the cables are properly connected to the system board from the hard drive, CD drive, and DVD drive. Check the computer message that appears on your monitor screen.
Dell
dell.com › support › kbdoc › en-us › 000126021 › a-reference-guide-to-the-dell-optiplex-diagnostic-indicators
A Reference Guide to the Dell OptiPlex Diagnostic Indicators | Dell US
This series had a combination of Power button LED states, and the A, B, C, D block was replaced with 1, 2, 3, 4 instead. The diagnostics LEDs moved from the rear of the chassis to the front under the audio ports.
Dell
dell.com › support › kbdoc › en-uk › 000126021 › a-reference-guide-to-the-dell-optiplex-diagnostic-indicators
A Reference Guide to the Dell OptiPlex Diagnostic Indicators | Dell UK
This series had a combination of Power button LED states, and the A, B, C, D block was replaced with 1, 2, 3, 4 instead. The diagnostics LEDs moved from the rear of the chassis to the front under the audio ports.
Reddit
reddit.com › r/dell › dell optiplex 790 lights 1 & 3
r/Dell on Reddit: Dell optiplex 790 lights 1 & 3
July 5, 2020 -
I’ve owned a dell optiplex 790 for a year, with an i5 2400 GTX 1050 and 16GB (4x 4GB). And as of today when trying to boot it’s powered on but has no display and has the power light orange and the numbers 1 and 3 flashing orange. I’ve tried reseating the RAM by that hasn’t fixed my problem, is there any other possible solutions.
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lights 1 and 3 are indeed a ram problem. Assuming you didn't add new ram: - check for debris or dirt in the ram slots - try to put only one pair of similar ram.
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I had the SAME issue and it turned out to be PSU issue. Replaced the PSU and PC works now. For testing I connected standard size PSU outside the case.
JustAnswer
justanswer.com › computer › fahk3-power-button-flashing-amber-green-lights.html
Troubleshooting Dell Optiplex Diagnostic Lights and Flashing Orange Light Issues
According to Dell diagnostic indicators, lights 1 & 3 suggest a RAM issue. A blinking orange power light indicates a failing or failed PSU. Please try re-seating the RAM chips one at a time, starting with no RAM, and see if the error persists.
Reddit
reddit.com › r/dell › dell precision t3500 diagnostic lights 123 and 2 short beeps
r/Dell on Reddit: Dell Precision T3500 Diagnostic Lights 123 and 2 short beeps
July 13, 2023 -
Hi guysI was hoping to get some helpI got this Dell Precision T3500. which has been working pretty well for a long time, but recently it decided to act up and now it won't boot and it gives me the 123 diagnostic lights error and just before that (or about the same time) it beeps twice (short beeps)
the manual was checked: https://dl.dell.com/manuals/all-products/esuprt_desktop/esuprtl_precision_workstation/precision-t3500_service%20manual_en-us.pdf and it says that the error means : ´other failure´
there's nothing for the 2 short beeps in the manual.
someone actually paid for some diagnostics online but that resulted in no resolution, that was posted here: https://www.justanswer.com/computer/9pq0y-dell-precision-t5500-post-error-leds-1-2-lit-power.html
here are my 2 cents becuase I figure someone might run into this problem again and there's no actual resolution posted anywhere as far as I could tell.
my resolution:
In my case, I had 4 GB of memory total: 2 sticks of 2gb each... the people that sold me this machine which I'm using as a firewall for a school (seems like an overkill) put in 2 different sets of memory, in any case the comptuer did work ok for years.. memory was detected.. all was fine but it appears that one of the memory sticks is the one causing the issue.
Once I figure out which memory stick seems ok.. I put that as the only ram stick and now my pfsense firewall is back to live... tomorrow I'm buying 8gb of memory (2 sticks of 4gb) to replace both sticks.. hopefully this can help someone.
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The same situation happened here. It worked, then I added a 2GB stick of RAM to the RAM I had. It showed me an error about changing memory configuration. I pressed continue, and it shut down. So, I pulled the extra stick out, and now when it's booting, it goes like 3, 4 then 1, 2, and then 1, 3, 4.
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Glad to hear you solved the problem. You did exactly what I would've recommended: pull out components one by one until you isolate the problem/faulty component. All hardware has a finite lifespan. It looks like your RAM stick has reached the end of its life.
Dell
dell.com › dell community › desktops › locked topics – desktops general
Dell Diagnostic lights 1-3-4? | DELL Technologies
September 7, 2009 - Power off and disconnect PC from the wall. Press/hold the power button on the tower for ~15 sec. Open the case and carefully<ADMIN NOTE: Broken link has been removed / replaced from this post by Dell>in their slots.
PC Outlet
pcoutlet.com › systems › laptops › fix-a-flashing-light-on-dell-laptop
Fix a Flashing Light on a Dell Laptop: Troubleshooting Guide - PC Outlet
April 22, 2025 - Many flashing light problems stem from simple user mistakes that can be easily prevented. ... Improper shutdown can corrupt system files, often leading to the dreaded “laptop won’t turn on” scenario with diagnostic lights flashing.
Reddit
reddit.com › r/dell › help with diagnostic lights
r/Dell on Reddit: Help with Diagnostic Lights
July 18, 2020 - I JUST HAD TO UNPLUG MY PSU for about 20 SECONDS.. and turned the PC back on AND IT doesn’t show the 2,3 or 2,3,4 anymore ... maybe you should think about replacing the bios battery, and if it's not done yet, update to the last bios from dell. I'm glad those lights are gone. If I recall correctly, in the bios -> system configuration -> peripherals: there you can check or uncheck things like sata 1 or floppy
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Solid amber on the MB means it has power. When the power button has blinking or solid amber, then it's a problem. From your photos it looks like you have the SFF model. Optiplex 780 Documentation From the 780 Service Manual: Optiplex 780 Tech Guide.pdf
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I mean look at these pictures
Dell
dell.com › dell community › desktops › locked topics – desktops general
Dell Diagnostic lights 1-3-4? | DELL Technologies
September 7, 2009 - Power off and disconnect PC from the wall. Press/hold the power button on the tower for ~15 sec. Open the case and carefully<ADMIN NOTE: Broken link has been removed / replaced from this post by Dell>in their slots.
Dell
dell.com › dell community › desktops › locked topics – desktops general
Dimension E520 won't boot - diagnostic lights 1,2,3 on. | DELL Technologies
June 16, 2008 - My Dell Dimenion E520 has suddenly stopped booting up - no recent changes to hardware have been made. Diagnostic lights 1,2,and 3 (not4) are coming on. No signal is output to the monitor - no Dell ...
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I didn’t see the usb on boot menu so i changed boot settings. 1 boot OS sata, 2 usb devices. All others disabled. After this i get no display signal, no mouse or keyboard signal even using an ps2 port. GPU is rtx 2070 ti. Ive tried removing motherboard battery and pressing power button for 30 sec but no success. Also tried an old gpu and same.
When i press power button light 3 and 4 come on. Than light 4 turn off 3 stays on. Than 123 lights stay on.
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You could try reseating RAM and replacing the CMOS battery, but normally this is a sign of a dead motherboard.
Dell
dell.com › dell community › desktops › optiplex desktops
Optiplex 3010 SFF won't boot, lights 1,2,3 and blue power LED | DELL Technologies
October 14, 2019 - Turned out that's what it was, the front USB panel failing. I know i tried or at least i THINK i tried just the rear USB only but for whatever reason it's working using the back panel now. Found a replacement on eBay, OEM for 8.95 so that will work.