"Rod" wrote in message

Had that recently - oddly enough, seemed to be the graphics card.
Remove, reseat. Update drivers. Update firmware (on card and/or BIOS on
motherboard). Most complete fix was to switch graphics cards between two
identical machines - problem moved with the card but also became much
less frequent (once a month instead of several times a day).

Other things tried w8ithout success (but might be worth a go) included
checking memory using http://www.memtest86.com/, reseating memory,
patching Windows, setting graphics acceleration to minimal and all the
usual silly things that almost never help.

--
Rod

Does your graphics card have a fan?