I had the same issue with the same board. Two things to do:-
1. Make sure you do not configure USB devices to sleep.
Check your power settings; on mine they were set to sleep by default so KB or mouse could not wake things up.
2. Go to the BIOS and disable the PLL Overvoltage
Seems totally unrelated, but it worked for me and many others
Since I have an unlocked processor looks like I will eventually have to choose overclocking vs sleep capability.