Re: eMachine beeps three times at start-up and nothing comes on the monitor.
A computer will POST even if the hard drive is removed, try what Tommy Boy said, remove the ram, inspect it, and reinsert it making sure it is in there the exact same way, also did you install any new hardware just before this started to happen???
So, remove RAM/Video card/any other PCI card, with no power to the system, then reinsert them.
If that don't work, try with just the RAM and video, if so then it is a different PCI card.