heh, I don't know about Emachines now, but the older ones are notorious for power supplies going out on them. To add insult to injury, the PS is proprietary, so you'll
a.) Have a hell of a time finding one that fits your case
b.) Buy a new case and PS, and migrate all your current parts... if they're compatible with the case. Usually there'* a standard for this, but no guarantees that Emachines or any big computer company will make computers that comply.
My uncle'* Celeron 533mhz Emachines has a PS that'* starting to go out. You'll be using it and bam, it shuts down or restarts