Xps 720 PLEASE HELP

I purchased a xps 720 about 2 years ago. After 6 months of owning it I started getting the TDR errors within minutes of gaming. After dell replaced my motherboard,ram,video card twice,hard drive, the problem was still not fixed. I then switched to windows XP, because it was the only known solution and it was fixed until I just recently reformatted. I reformatted with windows XP and now my PC just randomly restarts, or freezes with looping sound while gaming, but this doesn't happen everyday. I have checked the tempetures on everything inside my case and everything is great, I tried a kind of different ram, I tried under clocking my original ram also, I tried 3 DIFFERENT video cards and I even checked the voltage on my psu, 12V 5V and the 3V and they are all good. I am now completely out of Ideas. system specs are:

Intel core duo 2.6ghz

4 gigs corsair dominator ram,( i have tried 4 gigs of regular ram also)

8800gtx(I have tried 2 9800gt's also)

Seagate 250GIG HD

on board HD Audio

One thing I have noticed though is that one of the chipset's on the motherboard doesn't have a fan on it, which is normal, but it burns my fingers if I touch it. The video card runs no more than 55-60C under load and the cpu is no more than 48C under load (note: I am not always gaming when this happens, its just a random thing. Any help would be appreciated THANKS

Hey lonniek - could you give us more details about your PSU please? I had similar problems untill it failed... overheating may also be the reason as r_manic mentioned but I would also try with a different hard drive if I were you.

Thanks guys, The problem was the hard drive, I ran a test on it and it failed within minutes. I put a new hard drive in and haven't had a problem