Hey guys, I use a desktop Quad-Core Mac Pro for my recording studio business. I had a job yesterday, but I had to cancel it because of technical difficulties with my Mac Pro. I believe it is a 2011 model. Anyway, it wouldn't power up correctly. It made several unsuccessful attempts but failed to get as far as showing anything on my displays. The white power light on the front would come on but there was also a red light from behind the front grill. Sometimes, without touching it, it would continually turn itself on and off again and repeat the failed start ups on its own accord at random. At one stage I unplugged everything, including the power cable, and the red light remained on. Eventually I took off the side panel to have a look inside. Someone once told me that if the fans stop, the power cuts off as a safety mechanism. I made sure all fans were running. There was some dust in there, but it didn't look too bad, I've seen much worse. I removed the RAM memory sticks and re-seated them. Again, I tried to start it up and there was the same problems. Eventually, it refused to even attempt to start-up, no red light, no power light, just flat dead. When this happened, I decided to phone my local Apple store to make an appointment to have it checked out. I was told I needed to use the website to do so. The band I had in the studio were still there waiting to see if I could get it working again. I went back to the studio to explain to them what was happening. Before I phoned the Apple Store, I decided to try one last thing. I took the Hard Drive out and re-seated it. Then I did a full studio shut down. Turned all my monitors off, all my wall sockets. Then I put the Mac Pro side panel back on, I plugged everything back into the back of it, my two screens, my Firewire mixing desk, my keyboard and then tried for one final time to start it again. Bingo - this time it powered up 100% perfectly and ran for about 3 hrs, giving me enough time to back up all current studio work. After about 3 hrs of running smoothly I decided it was time to try shutting it down and restarting. Rather frustratingly, it worked perfectly. I shut the whole studio down, went back home for a bite to eat, and a few hours later returned and tried starting it up again. Its working fine now. I am quite irritated that I actually can't seem to find a problem with it now. Theres not much point taking it to the Apple Store as they'll find nothing out of sorts with it now. The reason I find this annoying, is because I have a lot of studio work coming up next week, and I will be waiting for it to let me down again at any second. Id like to hear the opinions of those who know more about these machines than I do. Is it possible that this was a one-off occurrence? Is it possible that I just needed to reseat my hard-drive and thats what fixed it? What would the chances be that it might be resolved now and never happen again? I'm just feeling really apprehensive about it letting me down again now. Many thanks, Steve.