is it a blown capacitor? HELP!!!!!

HEY GUYS,

I have an old 1.8 GHz iMac 17" G5. I had it plugs into the wall, an external drive, and the keyboard. I have had it on, working for almost 5 years. I am planning on selling it so today I backed it up, restored the OS and was installing iLife '09 for the person buying it. After the reboot from the install, the computer was sitting there, awake, and all of the sudden, IT WENT BLACK!!!! I tried to hit the power button multiple times but it just made a faint, high-pitched "charging noise" every time I touched the button. It was halfway between a beep and a buzz. I tried to unplug and replug it in, but it only whined every time I replugged it in. I called Apple and they said it was a blown capacitor in the power supply (requires $200 repair). Instead of just accepting it, I opened the iMac. There were no visibly blown capacitors, but the inside was full of about a cup of dust. I vacumed it out and the computer booted for the first time. The Apple guy said it could have overheated and if I let it run overnight and its still kicking in the morning, I'm good.

Does anyone know if I am in the clear or if it was just a temporary fix?

Thanks a lot