Fuzz on computer moniter, then computer wont boot...whats the problem?

The power light on the computer goes on....and everytime it does I always hear something spin and then a "beep". But today...all I heard was the spinning and no "beep" and the computer wont boot up. It started happening when I saw a colorful snow (like you do when you see snow on a tv screen) on the Moniter. I reload the computer and now it wont boot up..just a continuous spinning noise. Anybody know whats the problem? I have a emachine windows vista