5870 spontaneously reboots

[ViperV990]

Symptom:

The system stays stable for hours in TF2, but within minutes of getting back on the desktop, it will hard reboots.


What I've tested so far, without success:
- Disconnected the two mechanical drives
- Left out 1 of the RAM sticks at a time
- Swapped out PSU for an older unit
- Unplugged front panel USB and sound cables
- Uninstalled the ATI driver
- Reinstalled the ATI driver
- Booted into Ubuntu LiveUSB
- Unchecked "Automatically restart" in System Properties -> Startup and Recovery
- Reinstalled Win 7

It does NOT reboot if I go into safe mode.
It also does NOT reboot if I take out the 5870 and use the onboard video.

I noticed the card's cooler is quite hot to the touch - but that doesn't explain why it's fine in TF2. Fan seems to be doing its job: if I unplug the PCI-E power cables from the card and boot up the machine, the fan will spin at full speed - very loud and a lot of air.

Drivers are up to date.

Video card has never been overclocked.

I'm running out of ideas and am getting close to writing off the card


Specs:
i5-2500K
Gigabyte GA-Z68MX-UD2H-B3
2x4GB G.Skill DDR3 1333
Sapphire 5870 Vapor-X 1GB
Corsair TX750 V2
Intel X25M G2 80GB
2x WD Caviar Blue 640GB
In Win Dragon Slayer
Win 7 x64 SP1

 

[Zargon]

what case?

if you really think its the GPU you can always RMA it if its still under warranty

I've read/heard of some games(I think source games included) dont limit FPS in menus etc and driving the menus at 400+ FPS can freak the card out and cause crashes/glitches

section 8 prejudice does it to my 6950, if I leave the menus open too long it will flake out bad

 

[ViperV990]

I'll have to test leaving TF2 at its menu after I get home tonight.

Never deal with Sapphire's RMA process, and according to http://www.sapphiretech.com/presentation/support/?cid=3&psn=000203 I'll need to bring it back to where I bought it in the first place. Not sure if I can still find the receipt. Either way the RMA is likely to take weeks, and I doubt I can deal with not having a card for that long