Looks to me like a driver problem, try updating to either the latest drivers from the Nvidia website ot the Omega drivers click here personally I completed this game with no problems on my GeForce FX5900 using omegadrivers
You could try downloading driver cleaner from here click here after you use add remove programs to delete the driver and then reboot and then reinstall the graphics card drivers, I'm not 100% sure whats wrong but think that some part of the old drivers may have been left behind and may be causing the problem. If you can do a clean install of the latest drivers it may solve your problems.
I think if it is a motherboard problem you'll have to tell us what motherboard it actually is that you have in order for anyone to help. One question though is this a new graphics card? If it is and you have a similar problem playing other 3d intensive games it may be either a power supply problem as I presume the card has a seperate power connector as well as the power it gets from the slot or the card may be faulty. I bought a 9800Pro a few months ago and it would run games ok until I tried something like Farcry and then it crashed, I got another card and its fine now. Is it a new card?