What could possibly be wrong with my computer?

My computer has been running perfectly and I haven't been experiencing any problems whatsoever. I haven't downloaded anything in the past few days so it can't be a virus..( I don't think).. Today though when I opened Firefox it automatically checked the compatibility add-ons and started up fine. A few hours later I opened Firefox and I got a message that it crashed. Then instantaneously my computer crashed. When it went to reboot it stayed on the blue startup screen and my keyboard or mouse wouldn't work. Then I unplugged it, plugged it back in and it seemed to power up fine. I quickly noticed a problem because my computer was running yet my mouse,keyboard and monitor weren't receiving any power. I removed the CMOS battery for 5 minutes and it didn't fix anything. I have another computer and thought maybe it was the power supply. I swapped them real quick and the problem was still present so the power supply is fine. Next I plugged my hard drive into the other computer and it took me to the startup screen and suggested I launch startup repairs. I did that but after that it would try and restart but it seems like it's on a loop and keeps going back to the blue startup screen. I put in my repair disk and scanned it for memory errors. It came back with no problems but still won't startup. This leads me to believe that there is something else wrong in my computer other than the hard drive. I think my hard drive is ok even though it won't start up because it isn't configured to the computer I plugged it into..So here is my question. What can I do to determine the problem? And like I said I do have another computer, so if the computer is dead I don't care. I just want my files, so how would I get my files to another computer. In the case my hard drive is the problem and won't start up how can I get those files? They are very important and I'm freaking out...
My OS: 64 bit Windows 7.