I have an HP Probook 450 G1.
The laptop does not want to turn on, I can hear the fan spinning but there is no display (black screen). The wireless button is glowing orange and the caps lock light is continuously flashing. After some troubleshooting I discovered that the continuous flashing is a BIOS error, I replaced the CMOS battery and tried to turn it on again, it does the same as before - fan spins, wireless button glowing orange but no display.
The difference this time is that the caps lock button only blinks 3 times. I did some further troubleshooting it appears that the blinking indicates a corrupted BIOS.
I followed HP's advice and downloaded their BIOS update and recovery software and loaded it onto a flash.
They say that you should hold Win + B keys in while the flash is connected and press the power button, this will load the BIOS recovery program from the flash and restore the BIOS.

The problem is that none of the key combinations are working, I tried Win + B, Win + V and just the B button (these other 2 combinations from a YouTube video), it does not work.
Another suggestion was to connect a bootable flash with an OS on and try to enter the BIOS that way but that also did not work - the display remains black, I cant do anything.

Another thing to mention is that after a while of trying to get the recovery mode loading the caps lock stopped blinking 3 times. It does not blink anymore with a normal boot, or even with the USB drive in.
Now it's just black screen and orange wireless button. I though maybe the screen just died but I am not sure how to test that properly, tried VGA and HDMI cable to an external monitor but it just says "no source found".

It's worth noting the laptop came with Win 8, but it currently has Ubuntu installed.

other things I tried:
•hard reset
•boot without battery
•remove and reseat RAM.
•boot without HDD instated.

Hey all, I did something which is not at all recommended but didn't knew this at the time of doing. I update the bios to F.73 Rev.A and now my PC seems to be Bricked. It is starting but I am getting a blank display. At the time, BIOS was updating, I saw a failure message and after that the PC didn't turn on. I tried creating a bootable stick using the same bios from HP site but win+b key proved out to be a big scam. Need your help guys. What should I do, it's my friend's laptop? Any help will be appreciated. Model no: BS-579TX Windows ver: 10

SOVLED!

HP Pavillion x360 m1 Convertible PCModel: m1-u001dx

Tried to update BIOS, was connected to AC power, let it run and left the room once it started, came back to a black screen, but power light still on for about 20 minutes with no activity. Powered it down now it wont come back up.

When I press power, the power light comes on, i hear fans whir strongly at first, then slowly die to nothing after about 5 seconds. Screen never seems to even turn on, no logo, no BIOS menu.

Tried pressing Windows + B and Windows + V at startup, makes no difference, tried doing the same while plugged into an external monitor, no difference.

Is there anything else I can do?

EDIT (SOLVED): It looks like updating BIOS ruined my RAM. I removed it and replaced it with an old RAM stick I had lying around and it booted back up. I took the original RAM and put it in another working laptop and it created the exact same issue.

Thank you everyone for your help!