Listen for shorts or odd sounds when you turn it on. Make sure everything is plugged up correctly, if some how a ide cable came loose, in some cases it wont boot up. When I troubleshoot stuff like this, i just start pulling stuff, trying to boot the computer, pull something else out, try again, etc. . . untill I figure out what device was causing the issue. IMHO, if the power supply went out, the computer would have just shutoff, so I doubt its your powersupply, and in the 10 years I've been using computers, I've had only one go bad.