Hi,
I recently replaced my AMD HD5850 card with a Club3D G9 290x and I have the exact same problem described by the thread starter.
PC reboots randomly while in Windows. While playing Hearthstone the screen sometimes turns black for a second and comes back, and I've had a couple of BSOD while playing Hearthstone as well.
I have a 600w modular PSU. When the crashes started to happen I immediately thought it had to do with the PSU since I've never experienced crashes like this before with my HD5850 that has been running for 6 years without any issues.
The crashes never happened when I played Watch_Dogs all day long, which i thought was strange.
I have changed the GPU clock for 2D to maximum 600mhz with Asus GPU Tweak (instead of the default 300mhz), and been playing Hearthstone all day to check if my system would crash, but that didn't happen anymore.
If others could also try this and post their findings here, that would be great.
Edit:
Sorry to inform, but the BSOD still happens. Even bought a complete new PSU, CPU, Ram, MB, SSD and they still happen. I'm beginning to believe this is just a bad GPU release. Tried 2 diffetent R9 290x cards. Both BSOD with same error 0xa0000001 atikmdag.sys, ntoskrnl.exe.
Always when playing Hearthstone of browsing (youtube). Tried all drivers 13.2, 14.4, 14.6 with and without CCC. Reinstalled W7 10 times. Tried different VBIOS (asus, club3d). Problem still occurs.
I even tried installing W7 clean with ONLY the 14.4 driver and Hearthstone game. Still BSOD.