Have you changed anything? Hardware or software? I'm assuming that error was a Blue screen? Then after that windows would hang at the loading screen?
Only time I've had this happen was when I had a video driver conflict and when I had an IRQ conflict between 2 pci cards.
Try booting in safe mode (with networking). That will disable just about everything and let you get into windows. Go online and download the most recent drivers for your g-card from
www.nvidia.com. Go into your device manager (right click My computer---> manage---> device manager), find the vid card under Display adaptors and uninstall it (not just remove the driver). This way windows will auto detect it on next boot up and won't try and load a driver.
Then restart. If windows loads then cancle the auto driver install stuff and install the vid driver using the .exe file you downloaded.
You might also check the event viewer and see if windows logged the error. It's in computer managment too. It might tell you what screwed up.