I'd lay odds its the Geforce drivers. I couldnt tell you which one's to try first, The GF2 MX cards seem to be real tempermental sometimes.
Other things to try is making sure the card isnt sharing IRQs with any other device. If so, then move the conflicting card to a different PCI slot and try then. Also, if your running a VIA or AMD motherboard, try upgrading the AGP miniport.
Hope this helps.