Its not a driver issue. If he can get to the user screen, and then goes black when he logs in, its not a driver issue. A driver issue would usually cause Restarts, BSODs, or Nothing after the windows loading screen. Never come across a PC with a Video driver issue that prevented you from logging in.
But try starting up in safe mode. Pretty sure it will start up. If it doesn't then something is going on. Maybe bad hard drive as well.