It's a hardware conflict with some hastily-built systems that causes the card to lose its IRQ. There isn't much the driver can do about that. I learned that from dmesg or /var/log/messages output. When I log in remotely and try to rmmod and insmod the nvidia.ko kernel module it says it can no longer communicate with the card. The IRQ is gone! Try removing unnecessary devices or shuffling IRQs around in BIOS, save ESCD. Others have recommended using some sort of nVAGP option in xorg.conf I can't remember. If all else fails, add noapic to kernel line in grub.conf. That's the only thing that worked for me.