What have I broken graphics card issue

It started yesterday, my computer would no longer play video files, after updating to the newest forceware drivers, it plays audio from the file fine but no video, same in both Windows Media player and QuickTime. Before the update the system would lockup, blue screen, or the screen would collapse to a single white line across the middle of my screen.

When I cut the video hardware acceleration off, it would display a single image. When I reboot into VGA mode it plays fine.

I've checked to make sure the fan on the video card was still turning, and my computer hasn't over heated.

I'm running an Asus N6600 AGP video card, this card requires a direct power feed from the power supply, since it works in vga mode and the PS is nearly eight years old. I'm wondering which component I need to replace, video card PS or what? If the card were broke wouldn't I get other graphics problems?

Anyone know the solution for this?

Currently running forceware 93.71, updated from 81.98. Games run o.k., some lag, appears to be limited to video, looks like a software problem, but why does it affect different players.