|Did you try it with just the CPU in? |
If you get power with all the devices disconnected, that does kinda indicate one of the disconnected devices has a problem.
(edit) If you get beeps with the CPU installed, those are because of the missing RAM and/or graphics card.
If it will not come up with anything connected, my suspicion is that the power supply is defective. Too weak to supply enough power?
The three most important things in computing:
1. Backups, 2. Backups and 3. Backups.