Dell XPS 720 with a Intel Core 2 Quad Q6600, 1TB HDD, 3GB Ram, Nvidia GeForce 8800, Bios version A04.

It's having problems booting up. I will sometimes reboot a few times over and over until it freezes. It shuts off and freezes intermittently during the booting up process or if it happens to get further then the boot it freezes eventually. If I go into the bios setup it eventually freezes if I try to boot it eventually freezes it will often times freeze at random times during the bios screen or even not boot at all and just have a blinking "_".

I have reseated SATA cables, ram, cpu, and graphics card. I have individually tested the ram chips and it freezes in all configurations. I have swapped out the harddrive for a new one and it fails. I have tried to boot it up without the hard drive, dvd drive, etc in different configurations and it freezes each time. I have run the dell diagnostic disc several times it always freezes at one point or another. If i test the cpu it always freezes at APIC Mtest. If I run the system board test I get and "4C00-082D" error. I ran the symptom tree test on the system lock up symptom it passes everything and freezes on the "L2 Cache (Multiprocessor) - Alternating CPU writes test". Also the diagnostic lights sometimes but almost never read something like 123 or 34 but thats usually after I disconnected something or forgot to reconnect something more often then not they wont show up and the computer just freezes. Occasionally I've gotten a keyboard failure but have tried two different ones and seem to work fine so not sure if that matters or not.

I'm not sure whats wrong I believe I have tried everything short of replacing each part with a new one which would be way to expensive. So if anyone can point me in the right direction if  the cpu toast or is the motherboard done etc. I would greatly appreciate it. If there is something I am missing or another test i could perform please let me know.