Mirroring function on Apple TV 3gen not working - help please

I have a brand new Mac Book Air and recentlypurchased the Apple TV (3rd gen). The mirroring icon worked until I closed the screen on the laptop and then Apple TV stopped working on the tv I was streaming content to. I opened the screen and since then there is no mirroring icon in the upper tool bar. I rebooted my router a few times and still nothing. I can access my itunes content but not the mirror features.

Any help is appreciated.

Thanks