1)
http://www.tomshardware.com/forum/1436-73-shutdown-problem suggests the shutdown problem may result from a process becoming "stuck" on shutdown when an update is installed. It is recommended to run the command:
powercfg /energy
from an elevated Command Prompt (right-click on the Command Prompt icon and choose "Run as administrator") and examine the resulting report:
C:\Windows\system32\energy-report.html
2) In
http://www.overclock.net/t/1326292/cant-shut-down-windows-8-so-frustrating, a user reported he experienced the same shutdown behavior when attempting to shutdown an Ubuntu LiveCD session, indicating a hardware problem or that the issue resides in the BIOS. He ultimately resolved the issue by restoring BIOS defaults.
I found this interesting, because a user in a different thread reported the issue resulted from software used to charge devices from the computer. This could indicate ASUS Ai Charger Plus or the "USB Charge" setting in the G74SX BIOS. I believe ASUS has stated that Ai Charger Plus is incompatible with Windows 8 and should not be installed in a FAQ on the ASUS website. I'd also suspect the "USB Charge" setting in the BIOS should be disabled.
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT