my does my computer turn off by itself?

The problem with my computer is that when I turn it on it turns off by itself and thats when its standing up but when you lay it down it stays on for as long as I want, but when i have it laying down the CD drive won't work and the only way for it to work if my computer is standing. I've tried everything making sure everything is plugged in right and still doesn't work. Any suggestions?

kevin mojarro
November 2009