Shoutbox

http://msdn.microsoft.com/en-us/library/ms795930.aspx

http://support.microsoft.com/kb/834938

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I would suggest completely uninstalling the driver and reinstalling them (rather then just using the rollback), as well as trying a standard windows driver (instead of disabling your card). If that doesn't work I'd start looking into memory problems before trying to replace the gpu. You could always do a visual check to see if your card has overheated but I don't really think this is the problem.