Extremely frustrated right now. Me and one of my friends were completing my build and got most things to work. We were able to get the monitor to work and entered bios. Afterwards, we realized the hard drive was connected wrong, which is why our bios kept showing an error message. We rearranged some cables and plugged them into the correct slots on my motherboard. I attempted to boot the computer and it would not turn on. I'm sure that the cables are plugged into the right places, because it was working 10 minutes ago up until plugging in the hard drive. I tried to boot without the hard drive in and it wouldn't work either. The PSU is fine (I just ran a paperclip test) and the green light on the motherboard is lit up.
The case should have a fan with a molex connector too, not only 3 or 4-pin ( http://en.wikipedia.org/wiki/File:Molex_female_connecto... ).
Now, disconnect the fan from the motherboard (if connected there) and use the molex for connecting it to the power supply.
When starting the PSU by using the paperclip, not only the PSU fan should spin but also the one connected to the molex.