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.