Lumia 925 does not work, but without back cover it works

Hi,

can anyone give me an advice?

After falling down on the floor my Lumia stopped working. When I removed back cover it started to work, When I pushed the back cover on the sides it blacks out. I tried to run it without cover, it works ok. I found out, that it is the right lower corner of the battery, where I have to push to black out the phone. I started the phone (with the battery placed outside of the phone) and press the battery, nothing happened. I tried to press the phone in the place where the right lower corner used to be, nothing happened.

The only problem is that I can not use the phone with the back cover :-(