could be a driver issue, yah, but I doubt it. to check, go to my computer, software and de-install ALL Ati related things, then do a fresh install with the Catalyst 4.10. If that still does not work, I have no clue what it could be. I first thought of a heat-problem but you said the Doom 3 is running great.
May try re-install your mainboard drivers, but I'm kinda out of ideas. :/ Sorry and good luck though.

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