What happened when you turned on the power. Did you hear it try to start up? Did the light on front come on and start flashing?
If nothing happened when you pushed the 'ON' button, then you probably have a bad power supply and you'll need to look into it.
If it does try to boot up, and nothing happens after that, it could be the HD. Try swapping it out with a different HD and see if that boots up.
Jediwarrior