When switched on, chime and light appear, fan works then shuts down.
This is my first iMac g5 and i had a problem with it earlier where the screen would go strange colors after a certain period of time. i opened it and had a clean inside of it as i thought maybe the computer was overheating and switching off because of that.
but now after having reassembled it, when i hit the power button the computer makes the chime and the power light switches on and the fan starts working, then starts working even harder and then the whole machine immediately switches off. This all happens in about 2 seconds.