You can try either going back to an update prior to the latest if they have them archived or
remove all software and drivers for Windows to install only the basic drivers needed to see if this will help. Or you can go back to the original cd that came with the card to reistall the
software/drivers that came with that model card. Often the updates are for newer models
where they no longer run well on an older model due to be intended for those. ATI Radeon
cards see this all of the time.
Another item of possible concern here may have to do with the system memory or voltages
the bios is set at for the video card. After being taxed for a period having default voltage an
overheating of the card could very well cause distortion issues. When the card later cooled
or the system was restarted the normal screen appeared. If that is the case overheating is
a suspect there. Running a memory stress tester as well as taking a look at cpu and system
temps would also be advised here even though it is still pointing at the card itself.