I had the same problem but was able to fix it. Try this:
The problem seems to be with the battery connector onto the mother board. The reason it is looping is because it doesn't recognize the battery. While I had the phone open, I disconnected the battery and plugged the phone into the charger and pressed the on button. The phone continued to loop as it was doing before with the battery connected. While the phone was looping, I reconnected the battery a few times until the phone recognized the battery all of the sudden. After this the battery seem to work just fine. I quickly backed up the phone just in case (you should definitely do a back up before doing all this). Hope this helps.