For those running Asus P8 z77 MBs, you may see there is a new Bios Version 1805 2013.01.10 update available.
INSURE after installation, the Machine Bios is Reconfigured Back Exactly as you were running it BEFORE booting up in Windows OR you may have to Re-Activate the MS installation. (3 Day Warning)
NO problem calling MS for System Re-Activation except for the hassel of doing so.
The new Bios Revision 1805 with ( Enhance compatibility with some USB devices ) plus setting up the UEFI Bios sloppily can change the machine hardware configuration enough to cause the system to fall out of Activation.
By all means, don't let this posting scare you out of updating the machine Bios as Update #10 is Needed.
Note: The 1805 Bios Update doesn't appear to affect Windows 8.