Probably a bad motherboard... You could try removing components to see if it starts working, but I had the exact same problem with an older system once, and it was a dead motherboard... The system would turn on and off, but no video. CD-ROM's wouldn't eject/HD's wouldn't spin up unless they were disconnected.
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Desktop * Athlon X2 4200 | 2G RAM | 160G HD | 7600GT
Laptop1 * C2D T5550 | 3G RAM | 120G HD | Intel x3100
Laptop2 * C2D T5250 | 2G RAM | 160G HD | Intel x3100
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