It's unlikely to be a hardware problem since it was working just fine yesterday. Do you have the winxp cd? worst case scenario you could boot up with the cd and do a repair install. that only takes a couple of hours tops. Or if you want to keep poking around then you could boot into safe mode and try several things, like a virus scan, a spyware scan, and run the system file checker from a command line sfc /scannow it will probably take just as long to do either method, so it's up to you how much time you want to spend playing around with your computer. me personally i like to try to figure out what's wrong with it, but sometimes the faster method is just repair the installation and move on.