List the parts please.
Have you plugged the additional 4/8pin ATX in near the CPU socket?
Take the GPU out and try the onboard solution?

Try one RAM stick at a time in different slots.
Turn the power off and pull the battery out, go make some tea, refit and try again.
You need at least a single RAM, board, CPU+cooler to get to POST.
Cant be in a worse position than you in now.
Just use it enough to see if you get a POST screen.
Well thats kind of good news then, so you at least know the board/cpu/ram are ok now.