You're going to need to have someone take a look at your machine. If it won't even POST, there's not a lot of help we can give you. Obviously you should do the basics: move the computer to a new outlet and see if the problem persists; open the case and make sure all of the cables are seated correctly; check to make sure neither your RAM nor your processor have wiggled out of their slots.

And once that's done, take it someplace where they've got a full shelf of parts to slap in and see what the problem is.

Your hard drive is probably fine, so don't worry about losing your MP3s, school papers and pr0n. All of that will be easily recovered.