My CPU did that once. I just moved it and havn't had the same problem in a year...

Open your computer, get the compressed air, and fucking SPRAY THE FAN. Open it and SPRAY THAT SHIT. It helps, trust me. Also move it higher, or make it so its not so cramped. Think of it like this: If you're in a small place, and you cant breath the well, you're going to spaz out and start moving around. Thats how your comp is.