You should check to confirm that the ATKACPI driver is installed along with any other hotkey utilities. The Asus support website has downloads for these items depending on your operating system. Here is the url: [http://support.asus.com/download.aspx?SLanguage=en&m=UX31A&os=30|http://support.asus.com/download.aspx?SLanguage=en&m=UX31A&os=30]
At the top of the Downloads tab there is a drop-down to select your OS. The download you need is located in Utilities and it called; ATKACPI driver and hotkey-related utilities.
I hope this helps!
-TV