I have a g5 iMac that won't power on. When the power cord is plugged in, LED1 is on, which (according to the Apple support website) makes me think the power supply is ok. Correspondingly, I think the logic board must be bad. But I've replaced it twice now, and neither of the replacements has worked. Is there anything else that could prevent the machine from powering on other than the logic board or power supply? Is it possible that the power supply could be bad even though LED1 lights up when power is connected? Thanks for any help!