Background resorts to solid black. Tech worked remotely on system for over an hour, reinstalled Windows but problem not solved.

Try restoring the Windows theme first, because a solid black background after remote support work can be caused by personalization settings rather than display hardware.

1. Press Windows + R.
2. Paste this command and press Enter: shell:::{ED834ED6-4B5A-4bfe-8F11-A626DCB6A921}
3. In the old Personalization window, under Windows default, select Windows or Windows (light).
4. Restart the PC.

If the black background appears together with other display symptoms, reinstalling the graphics adapter is another supported step:

1. Open Device Manager.
2. Expand Display adapters.
3. Uninstall the graphics card.
4. Restart the PC.

If the issue continues, use the Windows repair option that reinstalls update components without affecting files, settings, or installed apps:

1. Open Settings.
2. Go to System > Recovery.
3. Select Reinstall now in Fix problems with Windows Updates.

If remote troubleshooting is needed again, use only trusted Microsoft remote-help methods such as Windows Remote Assistance or Quick Assist.

References:

• Background Is Black - Microsoft Q&A
• Screen turns black background with white text. - Microsoft Q&A
• Solve PC problems remotely with Remote Assistance