Since installing Windows 8, the computer hasn't been shutting down properly. When selecting to power down, the PC quickly displays the shutting down screen, the monitor powers off, and the computer remains on but unresponsive. After about 5 minutes, the computer will turn off. Upon booting into windows again, I am informed that Windows didn't properly shut down.

I'm running a fast SSD, and it's a clean install of Windows 8, so there's no way Windows is taking that time to do some sort of hibernate on shutdown or whatever - not to mention the error when entering Windows the next time.

This happens on every shut down. Restart works as expected.

EDIT: Formatting again didn't work. Fails regardless of drivers installed.

Event viewer

Always these two messages in close succession:

Error (event ID 6008): The previous system shutdown at 7:45:21 PM on ?27/?10/?2012 was unexpected.

Critical (kernel power, event ID 41): The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.