Vants, I renamed my machine and had no joy, but I did find this from some other post and the combination of YOUR and someone else's worked:
First, I setup iTunes sharing in preferences in iTunes, and like so many others, of course it did not work. I then signed out of iTunes on all of my devices and signed back in with no success. I reset my ATV, still with the same issue. I Had some time on my hands, so I made an install USB and blew away the partitions and did a CLEAN install of Yosemite and signed into iTunes using Preferences, Sharing, the usual way. I also renamed my machine in the sharing tab in System Preferences. When I went to Mavericks, the same exact thing happened and a clean install fixed it, but this was not the case with Yosemite. I searched the Apple KB and found this guys simple fix and it worked like a champ right away.
"Home sharing not working with ATV 3, Macbook Pro Retina Mid-2012. ATV's software is the latest and MBP is running Yosemite."
Activated Home-sharing via Preferences in iTunes and ATV can't find it.
Tried meanspa's solution and it worked.
To fix this, on your Mac's iTunes turn on Home-sharing via File > Home Sharing > Turn On Home Sharing.
After doing this, my computer's iTunes library popped up in ATV
**Under Preferences and Sharing in iTunes, It was showing that I was sharing my media, but when I went to File > Home Sharing > Turn on Home Sharing (in iTunes), I was not even signed into Home Sharing. Go Figure!? I do not know if it was the renaming of my PC AND signing in through the File menu that did it, but I can now see my media on all of my devices.**