Corrupt textures???

[Enkidoh]

If you're experiencing weird textures or 'visual artifacts' then usually that is a sign your video card is in trouble, either the drivers for it are buggy/need updating, or, more than likely, it's a sign of hardware failure in that the video card itself is dying a slow, painful death. I've found Nvidia cards are particularly prone to this kind of issue in that some minor texture tearing might first occur but gradually worsens the more time passes until finally the game becomes totally unplayable due to the graphics suddenly glitching out (I've had to replace 3 video cards in the past year due to similar issues, one of them an ATI Radeon card that just suddenly gave up the ghost with no warning, and 2 Geeforce cards that suffered similar issues to yours).

Replacing the card with a new one is really the only thing that can be done if it is indeed the video card failing, although updating your video card drivers may help too, if the cause is driver related.