I have an early 2008 Mac Pro that has recently developed a startup problem. When I press the power button it try's to start up for a few seconds then switches off. After a short wait and a few more attempts it try's harder (fans whirl, sometimes I get a chime, sometimes the Display even turns on) but then it cuts out and turns itself off again. It does this every morning, on several attempts, until after an hour or so it seems to get the message, start up and it'll work fine with no issues for the rest of the day. I've tried unplugging all peripherals. I've tried a fresh install of Snow Leopard. I've tried an SMC reset. I've tried zapping the PRAM. I've tried removing the internal battery, waiting, then putting it back in. I've checked that the RAM is seated properly and there are no red lights. I've reset the machine using the internal switch. I've pressed the Diagnostic button on the logic board and the LED's report no problems: Trickle power fine, regular power fine (when machine on), no nasty red lights indicating faults on the board, etc. So, my guess is that the Power Supply Unit is failing in some way and may need to be replaced. Does anyone else have any thoughts on this? Has anyone had the exact same problem and fixed it with a new PSU? I've had the Mac Pro only a couple of years and I'm out of warranty. I also have no Apple Care and would like some input before I splash out some cash (cash that I don't really have) Thanks in advance for any input, help and suggestions.