Hi

Welcome to Microsoft community.

I understand that you're having trouble with a black "APP Center" box appearing on your screen. This could be related to the Gigabyte App Center, which is a suite of utilities provided by Gigabyte for managing various aspects of their motherboards.

Here's how you can remove it:

1. End Task in Task Manager: Press Ctrl + Shift + Esc to open Task Manager. Look for any processes named "APP Center," "Gigabyte," or similar. Select the process and click "End Task."
2. Uninstall App Center: Press Win + R to open the Run dialog box, type "appwiz.cpl" and hit Enter to open Programs and Features. Look for "App Center" or "Gigabyte APP Center," select it, and click "Uninstall."
3. Disable Startup: Press Ctrl + Shift + Esc to open Task Manager and go to the "Startup" tab. Look for "APP Center" or any Gigabyte-related entries, select them, and click "Disable."
4. Registry Edit: Press Win + R, type "regedit," and hit Enter to open the Registry Editor. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run Look for any entries related to "APP Center" or Gigabyte and delete them. Be very careful when editing the registry, as deleting the wrong entries can cause system instability. Disclaimer: Generally, modifying registry subkeys or work group is intended for advanced users, administrators, and IT Professionals. It can help fix some problems, however, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For further protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click How to back up and restore the registry in Windows - Microsoft Support to view the article.
5. Check for Malware: Run a full system scan with your antivirus software. If you suspect that your computer may have been infected with a virus, it's important to take this step.

Remember to restart your PC after trying these steps to ensure any changes are correctly applied.

As for how it got on your PC, it's likely that it was either pre-installed on your system, or it was installed along with other software, possibly driver updates if you have a Gigabyte motherboard.

If you're still experiencing issues, it might be a good idea to reach out to Gigabyte support for further assistance.

Please let me know if you need any further assistance. Thank you. 

Best regards

Derrick Qian | Microsoft Community Support Specialist