Help? My computer is acting up!?

You've got what's commonly called the "Blue Screen of Death". It means that there is a critical hardware of software problem with your computer. It's impossible to tell you exactly how to fix it without you providing the entire error message. Your best bet is to start in safe mode, then do a system restore to before the problem occurred.

The next time you turn on your computer keep tapping F8 or F7 (can't remember which) while windows is loading. Use the arrow keys to select the option that says "start windows with settings from the last working moment" or something like that. If you don't get that option just go to safe mode.