I have the same problems.
A software update was available which I installed but had to reset all my credentials for the store etc. I played a tv show from my purchased items. It then wanted to do another update which finished and when I checked the version it was 4.4.2. I played a rental movie which initially indicated I was not authorised to play but on the second attempt it played. I have no idea what the intermediate software version was. However this time the settings were left alone. When I attempted to stream a downloaded TV Show from my computer I can now no longer stream content from my computer or iTunes. I can set my computer to Airplay to the ATV and it will show the TV Show from the computer using the ATV.
I have a second ATV which I have not updated yet. I will check to see if this is behaving in the same way with an older release.
The updated ATV will play music and display photos from my computer.
I suspect that iTunes is not authorising the ATV to play the content properly. This seems to be part of Apples many many problems with their iTunes authorisation process.
I must admit to not being very impressed with ATV 2, finding I had far less issues with the first iteration of this product. I can see me putting the old ones back into my system.
If anyone finds out whether this is a temporary iTunes issue or a ATV software issue, I would be grateful to hear from them. Meanwhile it is back to my Roku box and Amazon's Video on Demand which seems to be working fine (with no problems in the last year or so of use) and which has all the same TV programs I watch.