My PC has been running fine for a long time. Recently I upgraded the stock cooler to a beefier one. Today I decided to give the frequency a little nudge. On the second boot at this frequency, all appeared fine until the taskbar flashed about ten seconds into the PC being fully loaded up. It flashes black and then goes to the default windows opaque silver, and I can find no setting to change this. Troubleshooting and reverting the BIOS to stock conditions has not rectified the issue.
Sounds like a Windows file might of been damaged. Have you done a SFC /scannow in the command line?
If not that likely the drivers are acting up. I had something a little like this but it was with an Nvidia card and it was resolved after I re-installed the drivers.