Sapphire 5850 Xtreme hangs Win7 x64 randomly

[chungenhung]

Got a few Sapphire 5850 Xtreme that have some weird problems that i don't know what's causing it.
The system would hang randomly, and sometimes even reboot.
The system hanging is random. it can hang while booting up, entering the windows screen, runs fine for hrs then hang, runs fine for days then hang, etc. No consistency.

I've tested numerous ways, including fresh install of Win7, tried diff driver versions, lowered the GPU clocks, run at default clocks, test the card on other system etc. BTW, I've got 3 of these cards, and they all behave the same way. Since they run fine when tested on their own on other systems, the GPU hardware must be good.
The motherboard is also good, b/c it runs fine with other GPU installed.

All hardware seems to be good, as the card runs fine on other systems.
This is NOT a power supply issue, as I used a known good 900W unit.

Here is a link to problem complaining about the same issues that I am having:
http://www.tomshardware.com/forum/2852-63-5850-win7-driver-issues

I thought I would post here since a lot of people here use 5850 cards.
Any help would be greatly appreciated!

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[sadpandatech]

  Are you getting the pop up msg from taskbar stating that the driver crashed when this happens or is it 'hard' lockup with 0 messages?

  Has that fresh install of Win7 had the latest service pack applied?  Are there any yellow '!' for anything in device manager?
  What Cata ver are you using? Did you opt to not install the CCC (highly recommended to just install display driver and opencl stuff.)
  What chip set is the motherboard? Does it have a built in hdaudio chip? If it is an Intel ICH based board you may want to go to intel site and get the latest drivers from them as the mobo manufactures are notorius for not including the most receont ones.

  I am sure there are more things we can check, but that is a start.

[chungenhung]

yes, fresh install.
tried 10.7 all the way to 11 catalyst.
all just driver only.
sometimes it is hard lockup, other times it says driver crashed.
All the drivers are properly installed for audio and other things, no "!" in device manager.

[sadpandatech]

yes, fresh install.
tried 10.7 all the way to 11 catalyst.
all just driver only.
sometimes it is hard lockup, other times it says driver crashed.
All the drivers are properly installed for audio and other things, no "!" in device manager.

  good good.

  And the motherboard model?
  Have you tried 11.5+
  What software if any are you using to check or adjust clock settings, voltage etc?
  Have you run GPU-Z by Tech Power-Up or similar to verify the temps are normal and the cards are receiving healthy 12v rail voltage (11.7-12.1) is a fairly stable range.
  Have you checked the windows error logs?

  Get the windows updates, namely SP1 for win7.
  And if your mobo is using an ICH chip by Intel go to their site and get the latest drivers for it. I had to do this on a new Gigabyte whose included Intel drivers had bugs that Intel had fixed since its release.