回答先: iMac keeps Rebooting but LEDs and Voltage are fineI have the same problem of rebooting at start up. Consistently, it happens after startup progress bar in Yosemite goes a fraction of an inch. Then it reboots. It's the same thing every time I do it. The only thing that prevents it from happening is if I disconnect the smaller SATA connector from the hard drive. That will prevent the restart. I have tried very as hard drives with the same result. So this tells me that it is not the hard drive. I have also disconnected the power button to try and troubleshoot it. I get to see results with our without the power button wire plugged in. I've tried other wall outlets and powercords. I'm down to swapping out the power supply, but I think I should wait and swap out the sata cable first. Since that sata cable goes underneath the logic board, I would have to take out the board, Instead, I want to try and just run a new sata cable over the top of a lot of board between the hd and the board down at the bottom where it connects. That way I don't have to take out the logic...