Greetings and welcome to DriverHeaven!
First of all, it's really weird that your system is updating the WDM drivers with the Omegadrivers installed because the Omegadrivers do not include the WDM drivers. You have to download the appropriate version for the driver version you're using. Sooo...
This leads me to believe that you haven't successfully uninstalled any and all previous drivers....including the WDM drivers....from your system. OR, there are still Registry keys calling for the WDM drivers after you've installed new drivers.
You need to do a 'clean sweep' of the drivers related to your video card and include the WDM drivers, too.
Use the ADD/REMOVE Programs option to uninstall anything related to the ATI card. Do NOT reboot until everything is uninstalled.
AND, before rebooting, go into the Program Files and DELETE any folders that contain the Radeon Omegadrivers and any ATI official drivers.
NOW, ALSO before rebooting use CCleaner
CCleaner - Home to clean up the Registry. (Use the Issues option to do this.)
Now you can reboot but DO NOT let Windows install any drivers for the video card!! Cancel both prompts (one for Primary and two for Secondary) and simply let the system get back into Windows.
Run the Cleaner option of CCleaner.
Run the Issues option of CCleaner again...and again...until there are no more issues found.
Reboot once again. Do NOT let Windows install drivers for the video card. Cancel as above.
Once into Windows, begin the installation of your choice. For the WDM drivers, you will need to go to the ATI website and download the version related to the driver version of Omegadrivers.
Cheers and good luck!