I had the same problem, what I did;
# I followed the advice online of opening it, pull the flat battery cable, plug it in and re-attach the cable, nothing.
# I bought a second A2 since the first was covered under warranty anyway. I took out its battery, and put it in my old phone…. and voila. It worked. I than put the old battery in the new phone and…. voila it worked.
# I charged the old phone and the new phone, both gave a charging light while charging. I was all happy.
# Next morning old phone (with new battery) dead. Same problem as before. It charged overnight but thats it.
I assume that phone and battery got out of sync again. But there seems no way to fix it. It seem to loose its sync again. To backup data the above is a procedure, but I will now send back the old phone and continue with the new, which is also double the memory :)