We have a sticky that was created just to troubleshoot this exact problem. Please perform EVERY step in the PERFORM THESE STEPS before posting about boot/no video problems!
sticky and let us know how it goes.
One thing is for sure, your system doesn't have a chance of working without the 4-pin CPU power connector plugged in. That connector provides the CPU with power.
I can't stress enough how important it is to perform every step in the checklist, no matter how silly or trivial it seems.