APU's are bad, IMO. Just bad. Shame on AMD for trying to expand their selling range, and offering end-users a piece of scrap metal.
Updating the Display Driver -
did you check that there are no problems with that driver (check some forums)
Re-installing drivers -
Properly?
Memtest86+ -
How long?
New PSU -
What's the make and model of your PSU, and does it have any certifications (80 Plus Bronze/Silver/Gold etc.)
New install of Windows 7 -
Did this install encounter any errors? How did you install Windows?
The HD Audio driver is part of your display driver (believe it or not, or at least with NVIDIA products it is).
What I believe the problem to be? The APU. 100%, absolutely, all fingers from me, pointing at the APU. It's...