Ways to fix, i had this problem at different times, and these are the things that caused it:
1. Not enough RAM
2. How much HD space do you have? If you dont have enough it will do that.
3. Weak PSU (I had this problem when my PSU wouldnt was\'nt powerful enough for my Radeon9800pro)
4. Card not compatible with Driver.
5. Card not compatible with version of DirectX. (If im not mistaken GF4 is a DX7.0 card.
If i were you, i would get a new comp prety soon... and yes, i know you\'re not made of money.