I have a Dell Optiplex GX620. My computer wont turn on when I shut it down for a few minutes. When I press the ON button, the 3 and 4 light pattern lights up. To try and fix this, I reinstalled my RAM, but it still happened. So I then changed to 2GB of RAM, and the same problem still occurred. But the computer will turn on normally after several minutes. So I’m not sure what causes that.