Sometimes the level geometry isnt visible too...
I havent tried any other games yet.
It is a pretty old computer:
athlon xp 2000+
geforce 6600GT
win xp

Anyone an idea why this is happening?

Thanks

maybe because most computers suck my computer keeps crashing with games in fullscreen mode with the ati hd4850 card. its no obvious reason

I will assume you are running latest GeForce drivers and directX.

That being said, to me it looks like (most likely) faulty RAM on the video card.

Any chance of borrowing someone elses video-card to check?
I am not sure enough of this diagnosis to to just say "go buy a new Video-card".
Another GeForce card would be best as you wont need to load new drivers.

Could also be a bad game install, if it is only affecting one game.
Could also be 'too small' video-card if only 'newer' games are affected.

Best of luck dude...

I have almost the same problem with my HD4850X2, it runs super hot in fullscreen mode but runs perfectly in Window mode (or this fake-window-fullscreen mode).

well, on 9600 GT with the newest drivers , UT 2004 runs perfect - windowed or fullscreen

Yeah, but you gotta remember, Pupeteers 6600GT may be as "weak" as 128m ram.
I dont know the "system requirements" of UT2004. Does anyone? Preferably recommended.

Your 9600GT with 512M has MUCH more horsepower to play with.

And his CPU (Athalon 2000+) may be borderline specs for UT2004.

Hm Ut 04 should be working on it.
It is playable but i get these rendering errors.
(requires geforce 2 or higher)

ut 04 runs totally smooth with a 6600 gt and a 1,8 GHz pentium 4.

back in the day I played UT04 on my Geforce 440 with an AMD Athlon XP 2000+ smoothly with high (not highEST). Thats the nice thing about the unreal engine, works like a charm on almost any system.

I'm going with defective V-RAM or some problem with the motherboard... try borrowing another video card first, then you'll know for sure.

I had the same problem with a Sapphire GF 6600 GT in OpenGL using applications but only under Windows XP.
Also sometimes vertices werent textured anymore but painted in a random color - and it got worse the longer the application was running till it finally closed with an unkown error.
After I installed Win7 (and the latest OpenGL version) the problem was fixed...dont know what was really behind all this.