PowerPC :: Using IMac G5 With ISight Not Booting

I purchased the last generation iMac G5 when it came out a few years ago and I recently tried to sell it. I sent the item to the buyer and he said it would not start. The Apple logo or for that matter anything would not come up. He brought it to the Geek Squad at Best Buy and they said it was an issue that would most likely cost over $500 in repairs. I just got the computer back in the mail and all that happens when the power button is pressed is the white light on the front lower right hand corner comes on for a second, then the machine shuts down. You can also hear the machine begin to start for about two seconds, then it shuts down. Any ideas as to the problem and whether it is fixable without expensive repair costs?