My dad has a HP pavilion laptop, which is over 6 years old. It contains an onboard graphic card, a NVidia GeForce 8400M GS. Since a week or two, he's getting BSOD in Windows Vista. Also, the screen was acting up; strange lines and figures keep creeping up, but only once in a while -- not always. Thinking that it might be the drivers he had recently upgraded, I decided to downgrade the driver, with no luck at all. I then continued to deinstall the driver, and reinstalling the current stable version, but alas, to no prevail.

Windows kept crashing during the course of the last two weeks, and thinking it might be Windows breaking up, I decided to upgrade his Vista installation to Windows 7, as I've been hearing good things about it. Alas, even that didn't help, and it seems the strange lines and figures keep popping up. I've opened the laptop itself, thinking it might simply be overheating because of clogging in the vents, but that's not the case, it's clean as a whistle.

Now for the actual question; does anyone have a decent flowchart on how to troubleshoot such issues? It might well be the videocard itself, as the strange lines and figures sometimes even appear during BIOS and POST, but I'm not sure.