iphone 4s has stopped completely after ios8.2 update

I received my first apple device as a gift one day ago. An iphone 4S based on iOS7.1! After setting back to delivery status I have checked for updates. iOS8.2 was offered and I started the update. Download works and installation began. After finishing - apple sign disappeared and nothing works anymore.

When I try to connect to itunes error message 0xE8000084 appears but neither any connection is possible nor any action with the buttons of the phone is possible.

Before the update the phone was working and now I got crazy to loose the phone...

What can I do? Please help me if somebody can.

Thanks in advance