Apple TV 3 Home Sharing stops when I turn on another computer

I just got a Apple TV 3 and have it all set up and working.

I have it connected to my main iMac and Home Sharing is turned on for this computer.

But when ever I turn my Macbook Air on (Home Sharing is not turned on) the Home Sharing with the iMac and the Apple TV unit fails.

All computers and the Apple TV are using the same Wi Fi network and it is a Apple Time Capsule Wi Fi network.

Any help would be appreciated.

Should Home Sharing be on for all computers??