Computer Reassembly

Once again, get you anti-static bracelet on.  Clip it to your case.
Your hard drive must be replaced into it's metal setting and replaced it's down position.  With it's BERG cablere-attached.
Your RAM must also be completely re-attached and hooked in.
Your MOLEX cable must be plugged into the floppy drive.
Your PAT cable, as well, must be plugged in in order for your computer to work.
All BERG, MOLEX and such cables must be plugged back into your motherboard.

You then need to plug in your mouse and keyboard into the back of your computer.  Plug the PC into an outlet, get a monitor, plug it in. It should be functional once you hit the power button.