Sounds more like a problem with the PS. Is it brand new? DO you have an older computer you could try it in? Your saying that without the GPU installed, it starts up only with the four pin connector? I don't see how the eight pin CPU plug could stop it from working. I just looked at your MB on Asus's site. I had a weird "no video at boot" problem with an Asus MB on initial setup with the EPU and TPU switch and found out that they must be off until you install the AI suite. It was an older generation, this gen MB could be different, but just something to check. Your MB does have the 4 LED's at start up that indicate if the CPU, RAM, GPU and HD are all detected. THey should turn on at boot and then turn off. IS the CPU light staying ON. What is their status on each?