Screen resolution locked

The oddest thing happened yesterday, my screen resolution appears to be locked to 1280x1024(Native). Normally that would not be an issue, but, I like to play full screen video games which usually are at a lower resolution. Before yesterday, Descent 3, Diablo II, Battlezone II would all play fine, Diablo I had color issues. While I was trying to correct Diablo I, the screen first locked into 8-bit color. When I fixed that, the resolution is now locked into 1280x1024. So when starting any game, the display is a small box in the center of the screen, the size depending on the chosen resolution for the game, in the case of Diablo I, (640x480) very small. My video card is a Zotec nVidia GeForce 8400GS, and I have tried the easy stuff, update drivers, use windows troubleshooter, etc. I consider myself fairly knowledgeable, but this has me stumped. Does anyone know if there is a registry entry or .inf entry that could cause this?

OK, here's an update, apparently I did not re-install the video driver as I should have. This time I selected the "clean install" option for version 270.61 of the nVidia driver. I saw this possible solution from others that had some problems and decided to try it. I have not tried my games yet, but at least I can change resolution and have the display full.