Problem with my Galaxy S2 (battery heating error)

I have a problem with my Galaxy S2.
1. I can start the phone ONLY in ”HARD RESET” mode, and then choose ”reeboot system now”.
2. When the phone is started, battery is discharging very fast
3. When I try to connect via USB with computer, it,s says ”It’s allready conencted – Please disconect USB cable”. If I disconect the cable, the messege still remains.

I think the battery or motherboard is in short circuit, but I’m not sure. Or the battery be damaged? (I bought a new original battery 2 weeks ago)
I attached 1 photo with battery heating messege.
I allready done a HARD RESET, but no success.

Please if enybody has before this problem, or have an ideea, answer me 🙂