Question Computer will not boot back up after new parts/put back together.

[Zeitgeon]

I had recently bought a new cpu, mobo, and ram to upgrade my computer. When I put all the parts in, I got zero response trying to turn it on. When I unplugged everything but the mobo, it turned on. I tried putting all the old parts back in instead and same issue. Any help on what is going on? I can post pics or build details if needed.

 

[rgd1101]

full system spec? include make and model of the psu