Problem with Parallels Desktop 3.0 and Windows Vista

I have Parallels Desktop 3.0 with Vista installed. It was working fine before, but a few days ago I tried to start up the VM and got the infamous blue screen of death with the error message "The video driver failed to initialize." I don't remember installing any new software or doing anything different to cause this. I tried restarting and trying safe mode and all those options, but keep getting the same thing. The Vista install disk didn't do anything, and I couldn't find any solutions on Google. Can somebody help me with this? I use a crappy Windows-only homeschooling program and I don't want to lose half a year of completed assignments.

Try starting it in Safe Mode and see if the non-Parallels driver will let it start up.

If it does, the first thing I'd suggest is backing up your data, as running VMs is unreliable at the best of times, and your Windows install can be easily messed up, as you've found.