I have a pre built Dell computer from 2007 and I decided to take it apart to see if I could put it black together.. I put the components into the case and the power supply is hooked up to the motherboard, cpu, hard drive, and disk drive. However, when I plug it into the wall.. The computer makes a humming noise and off after about 5 seconds of being on.. It then turns on again and then turns off.. Nothing shows up on the monitor and a yellow low comes on the motherboard as soon as I plug the computer into the wall. HELP