Problems rebooting computer with ASUS HD 6870

[Lethargy]

I recently built a new computer. Here are my components:
PSU: Tagan TG800-BZ
MB: Asus p6T Deluxe V2
CPU: Intel core i7 950 clocked to 4GHz
HDD: OCZ revodrive 120gb and samsung spinpoint 2tb
RAM: Corsair XMS3 3x2GB DDR3 1600MHz
GPU: ASUS EAH6870 1GB DDR5 (radeon hd 6870)
OS: windows 7 64-bit

My problem is that if my GPU is warm my computer will refuse to start and I will hear 4 beeps. If I replace the GPU with my previous GPU (hd4870) or wait 15 minutes everything starts fine. The HD 4870 also reboots when warm.

I have updated my BIOS, double checked that every power cord is in place and even switched positions of the cords on my PSU, yet the problem still persists. What is wrong and is there anything I can do?

 

[wa1]

You can find what means by "4 beeps" on your mobo manual...

 

[Lethargy]

That just means "No VGA detected".

 

[Dogsnake]

Assuming you have proper ventilation, it is entirely possible the 6870 is defective. Is the 6870 O.C.'d? You can check the cards sensor readings using CCC. What do you mean by warm? Does the card work at first boot? If it does and then dies after some use, it is probably defective. When it heats up the bad component fails or it might be a connection (solder) that expands when hot and opens. Just as a check, you might set all you bios values to default and see if the card works. Don't know your O.C. settings but you may have affected the values to the slots?

 

[Lethargy]

Actually I'm starting to believe it's not a heat issue at all. Usually after having to restart my computer I've switched out my GPU to my old one. Now my card wouldn't start when it was cold, as in computer hadn't been on for 3 hours. I unplugged and pulled out my GPU and then plugged it in again and it was working.

I've clocked it through catalyst control center, but not much. 915MHz GPU and 1050 MHz for memory as default settings. CLocked to 975 and 1100 respectively.