Start with the bare bones minimum: Motherboard, CPU, RAM, PSU, Video, Keyboard, Mouse and Monitor. (No drives yet).

Flip it on and reset the BIOS to factory defaults.

Flip it off and connect one CD/DVD drive and one hard drive.

Flip it on and see if the HD is being detected in the BIOS.

* If not, there is a problem somewhere that must be resolved before attempting to go any further.

* If it is being detected, while you're there in the BIOS Setup make sure it's set to try and boot from the CD/DVD drive first.

Power down, insert a Windows 7 (or 8) CD/DVD and power back up. With any luck you should see the Windows installation routine starting up and eventually discovering your hard drive. Just follow along with the onscreen instructions from there.

Let us know what happens ...