My sister-in-Law just got a new iMac after previously owning a PowerPC iMac..I know about time right?? Anyway. I set up the new iMac and transferred all her iTunes data to the new mac but I can't get the AppleTV 2gen to recognize that home sharing is indeed turned on. Both are on the same network, it worked fine on the previous mac. I even restored the AppleTV and set it up as new and still it tells me to turn on Home sharing on the mac. Any ideas?
I had the same problem. Possible fix here.
Since installing 5.1 on my Apple TV 2 and Mountain Lion on my iMac, I wasn't able to use Home Sharing properly. This went on for two weeks, so I started looking for a solution.
On my Mac, I went into System Preferences, and Internet Sharing. Under wi-fi options, I changed the security from WPA2 Personal back to 128-bit WEP, which it was before. You'll notice when you go in that 128-bit WEP doesn't initially appear. But hold the option key and click the security dropdown, and it will. Then set your password, click apply, and you're away. My Apple TV is almost back to normal. Still seems a little slower, but at least it can see Home Sharing now and I can watch what I want again.
Funny, I still have to turn my Internet Sharing off and on again to get my iMac's wifi working. Mountain Lion seems to have stuffed that right up. But hope the Home Sharing thing works for you.