Am dealing with the same problem too. In my case though I am pretty sure I assembled it correctly taking enough time on my hands. In your case as you have said the PC is not starting up is it not booting or you cant even get the power on? My PC is powering up though but just before loading the OS it gives me a message "Lsass.exe object not found" and shuts down.
I tried last known good configuration, safe mode etc but the problem persisted. Just before I reassembled it things were working fine for me. I am at my wits end now trying to find where could I have gone wrong.