When I originally purchased my Mac Pro 3,1 I had installed a 3870 in it. It served me ok for a while but then I started having all of these random issues with the machine locking up. When it would lock up, sometimes it would give me a lot of problems starting back up again. So I spent the cash and upgraded to a 5870. Everything was for with it for a few months but now I am having issues with the machine just shutting off what seems like randomly. I could come back to the machine from it being idle for a few hours, move the mouse ... click on something that boom it turns off. When I got home today I logged back in, checked my email for 25 mins then out of no where it shut off. I can generally play WoW for an hour or two before it shuts down, but loading Starcraft 2 causes it to shutdown every single time. I am thinking it could be a bad PSU. I did an SMC reset, that didn't fix it and I have also tried disabling the hard drives from sleeping. I am suspecting that the shutdown _might_ be caused when the drives try to spin up from sleep mode. I just made that change a little while ago so not sure what effect it will have on it. Anyway, is there anything else that I could try ? I am gonna make an appointment at the Apple store, but need to find someone to help me bring it there. I have a bad back and can't carry the machine very far. Trying to either fix it my self or find something to help me hold over until I can get it there. Thanks!