graphic card works no more with videogames

Hello
I must say that I'm not sure if the problem is the graphic card, but when I try to play any videogame I'm not able to see anything. The writings disappear, the textures are all wrong and so on. Then, when I try to quit the game, somtimes the pc remains stuck and I have to reset it.
I use an NVidia GEForce 8600 gts, on an asus pk5 with windows xp sp3, and the drivers are all up to date (except for a device called "Microsoft dls Kernel Synthetizer", I was not able to find drivers for this but the pc used to work perfectly until now)

Here are some screenshots of the problem in his "weaker" form, but it's usually worse than this
[img=http://img43.imageshack.us/img43/9489/wowscrnshot101009025430.jpg]
[img=http://img21.imageshack.us/img21/1575/wowscrnshot101109034155.jpg]


Help me please, thank you