DRIVER_POWER_STATE_FAILURE (9f)

In order to speed up my SSD I did a few tweaks using tools from Guru3d.com. I also disabled hibernation using the command prompt thing. Have also been messing around with file page size and virtual memory to improve shutdown speeds. The hangs started at that time. It was immediately after the failed SSD upgrade. I did notice that the Asus USB driver has two setup applications. Installed both of them and so far so good. But the shutdown hangs are intermittent anyway. Uploaded the latest zip.file. I'll see how I do for a few days before resorting to a fresh Windows upgrade. Would like to get to the bottom of this myself. Cheers.

Ok mate. Just got a hang. Will try that.

Tried that, disabled Bluetooth (was disabled) and Atheros. Only have the anti-virus loading, getting constant hangs on shutdowns now. Disable anti-virus on start-up?

OK I think you need to use the removal tool which has repair and uninstall on it (smaller file, the drivers as I mentioned have two setup.exe files) then either repair or uninstall the driver because it is the same as the one currently installed. If the latter than obviously reinstall the bigger setup.exe. If this fixes it, ill flag the issue as solved. Cheers again.

This article helped

:) OK quick update. It started hanging again. But, BUT, I've now had several shutdowns without a hang. What I did was uninstall the Asmedia ASM104x Usb Host Controller (it will be at the top of your list of installed programs, provided you've updated it as recommended). Then I let Windows search for the correct driver. It will point you to one directly from the vendor. It has none of the bloat of the one on the Asus site. Simply install that. So far so good...Fingers crossed. Cheers for the help mate, and pointing me in the right direction.

Cheers Arc. No more shutdown hangs.