Let me start off here... XP Pro, 2.8G, 1Gig RAM, 5 year old E-machine which mother board I've replaced since then. Two days ago my computer wasn't working and gave me a Unmountable STOP Error blue screen. So I fixed that by repairing my Master boot record, but after that I had my computer up and running. So I took this time to defrag my computer, so I left to work while it was defraging when I came back I turned on the monitor to see if it was done(which it should have been by that time several hours later) and found my computer off altogether. So I started checking a few things and when I turned on my computer my monitor would not get a signal and it would give me three POST beeps about 3 seconds long each, but the CPU Fan would come on and my hard drives sounded like they were working and the PSU fan would come on. So I figured it was my CPU that over heated or shorted out, I had in the past never had luck with my mother board. Then I went and got another CPU and replaced it in my computer re hooked everything back up and turned it on it sounded like it was working but again I got one POST beep and then my computer will turn off. And again the monitor would not get a signal for the 5 seconds total its on, after thinking about it I'm thinking that it might be a PSU issue but I will have to wait till I get another one to test it out. If any one has any suggestions about my perdiciment I would love to hear it, and I'm sorry if I wasn't clear enough in the issue(I hate it to when people tell me about there computers and they don't know what there talking about) Thanks again to any one that can help.