I had this long running problem for over a year, and it drove me NUTS.
Aero would stop working if I hibernated my PC, or switched user.
I Googled, a lot, learnt a lot, WDM (Windows Desktop Manager) service, etc. but nothing worked. Microsoft’s own tool said there was nothing wrong. Stop the WDM service, re-start it, nothing.
Log out, log back in all fine. But very occasionally, I’d just be using the PC, and Aero would stop. Yet I could run any game, no problems.
So I installed Windows 7 again to a different partition, and then tried that installation of Windows 7, again same problem!
Obviously all service pack and updates applied, no solution.
The graphics card was upgraded, from an ATI Radeon HD5750 to HD6850, STILL no change.
Then I tired one of my children’s NVidia cards, still no change.
Then I upgraded my hard drive, still no change.
Then I upgraded mother CPU and RAM, still no change!
I gave up.
And then, almost a year later, my EZ Cool PSU died (diagnosing THAT is another painful story).
I fished out an old 550W PSU, nice and noisy, and guess what, the Aero crashing problem is gone!
It was The PSU! I did think for few fleeting moments that it maybe sometime ago, and then thought, don’t be ridiculous.
But there you go, if your Aero crashes a lot, it maybe the PSU, as it was in my case.
But alas, for all my love of Aero, Microsoft has removed it in Windows 8. I am not grateful or happy at that. Then again, my thoughts on Windows 8, after trying it out for a few weeks are, well, quite negative. I have no intention of going for it, unless sometime in the future I end up with a laptop for which no Windows 7 drivers are available. Then again if the laptop won’t run the odd game (I play about 2 to completion in a year, Skyrim is the most recent) I want to play, I’d happily stick Linux on it (Mint, not Ubuntu, as its Unity UI is as sucky as Windows 8 IMHO, well NOT so IMHO).