Dell XPS 730X not displaying

Okay so I recently bought a dell xps 730x gaming desktop from a friend. There was a problem with it. He sold it to me for cheap because of it. When I went to turn it on, it would turn onand then it would shut back down while not displaying anything on the monitor. I fixed the turn off problem by buying a new mobo. I installed the new mobo (Asus rampage 2,extreme). When I turned it on, it turned on but the monitor did not display anything. I tried a new GPU, I breadboxed it, I bought a brand new 1200 watt corsair power supply, and I tried different ram sticks. None of this worked. Oh and by the way, with the new mobo, the power button did not start it. I had to press the start button on the mobo because the connector for the front panel was incorrect. Depending on the pin arrangement, it would work but it would do the shut down thing. It did a boot cycle repeat by the way. It did not just shut down. I have now tried everything but one thing; the CPU. I think I am going to buy one but first I would greatly appreciate it if some of you guys could analyze my symptoms and diagnose it to make sure that the CPU is the problem.

So I have a few questions. 1. Is it the CPU. 

2. What can i do to fix the power button problem? Can I buy an adapter?

3. Is there any other problems that might arousing?

4. What things did I not need? In other words, what steps were unnecessary?

I did not go cheap when I bought the supplies.

The desktop has an

i7 960 CPU

A nvidia Gtx 640 Gpu with 2 gigs of vram- $150

In have corsair vengeance ram-$?

I have an Asus rampage 2 extreme mobo- $300

I have a raidmax rx-1200ae 1200,watt psu- $250

Thanks and all help is appreciated!