I too have this problem. I originally contacted Apple support on 3/22/16 and was advised to "keep trying" the activation process. Well, after 2 days of trying to get my iPad 2 to activate, and trying everything short of a total "Restore," I contacted Apple support again, today. I was able to speak with a senior advisor and he informed me that Apple is aware of this issue with iOS 9.3 and the iPad 2. Per this advisor the issue is Apple's problem and they are working on it. He says to look for 1) an update to iTunes that will allow iTunes to see your connected iPad 2, 2) the ability to choose the "UPDATE" option without going in to DFU mode, 3) an update to iOS 9.3 probably 9.3.1, 4) an internal Apple Server update, and 5) possibly all of the above.
Bottom line, if you have an iPad 2 and you have not updated to iOS 9.3, DON'T UPGRADE YET. Wait until you see an iOS 9.3.x update posted.
Gruene Guy