Originally Posted by heisenburg
My 2008 Mac Pro refuses to power on, when I push the power button nothing happens.No lights or fans power on; it acts like it is unplugged, but it is not unplugged. I tested the power cord in an another machine, and it worked fine. At this point, I'm thinking I will need to replace the power supply. Has anyone else had this issue?
Try unplugging EVERYTHING from the machine (all USB, monitors, ethernet, etc.) then plug power cord directly into a tested & working outlet. If the machine doesn't power on at that point, then it's probably the PSU. Can try unseating all PCI cards as well, but that's only caused a power issue for me once on a PC many years ago.
If replacing PSU yourself, be sure to get the right part number, they're all a little different...