MacBook – Keyboard shortcut to turn off display not possible with MacBook Air

I'm using a MacBook Air 2012 with Mountain Lion, and the new keyboard shortcut is:

Control+Shift+Power

If you run following command in the Terminal app it will show you what keep it from sleeping.

pmset -g assertions

Then based on the result you can take a action.

Here is a example:

pid 251(coreaudiod): [0x0000000100000d01] 00:17:27 NoIdleSleepAssertion named: "com.apple.audio.'AppleHDAEngineOutput:1B,0,1,1:0'.noidlesleep" 
pid 251(coreaudiod): [0x0000000100000929] 01:11:47 NoIdleSleepAssertion named: "com.apple.audio.'BoomEngine:0'.noidlesleep"

In this case it was the "BoomEngine app" preventing the sleep.

In your case:

You have the "magicwake" which is keeping it from sleeping.

That could be a Bluetoot coming from headset or external keyboard(track pad), or the battery is low.

It could be also a app that you installed that would wake up on network access.