Your shiny new ATI Radeon HD2900 Pro was installed with the latest drivers and or catalyst control center. You also installed the newest WDM drivers, but your computer hangs on shutdown and flashes a Blue Screen of Death (BSoD) before rebooting itself. You may also have an unknown acpi compliant device listed as being on the Radeon HD 2900 Pro under the device manager listing. Uninstalling the ATI drivers makes the computer shut down properly, but reinstalling them brings the issue back.
Ensure that your motherboard chipset drivers are up to date as a prerequisite. Also get all your Windows Updates. Reboot if needed, then install updated ATI drivers, WDM drivers, and get the updated HDMI Audio driver.
If you can't resolve the issue this way, try the other driver on the HDMI Audio Driver page. I have no idea why the HDMI audio driver is so buried on the site.