Trying to help my brother with his HP Pavilion a6720y pc. The Problem is a black screen at windows(vista) start up. The problem started when he attempted to install a video card. I have attempted to reinstall with his restore disks and with my own windows cd, continue to get black screen. I have read that it may be a driver issue. Not sure what to do next, as I can't see the screen to do anything. I have removed the video card, thinking it may eliminate the problem... Didn't help. Advice?