Your solution appears to have have solved this issue for me though the only way to wake this IMac is to touch the power button, the mouse and keyboard no longer awaken it for some reason. But that's trivial, I use Windows for only chat and gaming software anyway. I just like to be able to use the sleep mode just so I don't have to shut it down all the time. Thanks again for solving this issue for me.
The problem is under certain configurations the discrete graphics device (AMD radeon in my case) and the Intel GPU driver will conflict with each other and cause a crash in idgkmd32.sys. The Intel device would show up mysteriously after the system wakes from sleep. This problem has plagued my Windows system system since I purchased my iMac in 2011 with a Windows 7 installation and it persisted all the way to Windows 8.1.
The solution is to "completely" uninstall the Intel Graphics driver! Here is how to do it:
1. Go to the Control Panel.
2. Go to System and Security
3. Go To System
4. On the left pane go to Device Manager
5. In the Device Manager's menu select View and Show Hidden Devices
6. Go to Display Adapters you should see Intel HD Graphics (looks transparent)
7. Right Click on Intel HD Graphics and select Uninstall
*8. Make sure you click on "Delete the driver software for this device" (otherwise it will re-install itself).
9. Click OK and the issue should be resolved.
* Don't skip step 8!