Do you have an AMD graphics card (Radeon). If so, this may (or may not) help. Try turning off GPU Acceleration. (Preferences>Video). If you can't open Vegas do you have AMD Catalyst installed. Flying on memory here as I haven't had an AMD card for a while and it also may depend on the Catalyst version you have but if so look in the Power settings for something like Switchable Graphics Application Settings. There should be an option to set the performance level for Vegas - set to High Performance. Hopefully you can then start Vegas and turn off GPU acceleration.

Cheers, Robbie