Earlier today I was poking around inside my Mac Pro while waiting for my 4890. I decided to pull out the optical drive bay and see if I could remove the power cords plugged into the PSU. Only took out one, but I put it back in, made sure all four cords were seated, and tried turning it on. All I get is a clicking noise coming from around where the power cord on the back is. A 'click-click-click' that continues until I unplug the cord. I don't get a startup chime or anything else. Before today the machine worked perfectly. Any ideas on what I've done wrong and how to fix it? Any other information that I need to provide?