Doesn't sound like drivers if the pc won't boot. It sounds like an AGP port problem (assuming it is an AGP card). What you may need to do is check the voltage for I/O. You should be able to do this in the BIOS. So the problem lies with the motherboard. What make is it? Have you checked for a BIOS update? The BIOS update may address the problem, failing that you will have to change the motherboard. The problem is 2 fold the newer AGP cards are extremely power hungry and sensitive if it's not right ot won't work. Although the MOB says it is AGP compliant what happened is the MOB manufacturers only just met the specs and unfortunately this isn't good enough for the newer power hungry cards. You can get around this by replacing power regulators on the MOB, not recommended.
Hope that helps.
ps the above url should be
www.nvidia.com