I did the steps suggested by JeffreyV1 and it worked out!!
Thanks for sharing this @JeffreyV1!! Now my camera is back again!
So the problem for me was that the camera wasnt connected to the motherboard. These very small "metal surfaces" that connects the camera to the device have to be connected correctly. Somehow this didnt happend when i just tried to screw back the motherboard, after replacing the battery.
Here is a step by step guide of what I did to get it working:
1) Remove the motherboard and take it out of the case.
2) Remove the camera by removing a screw on top of "the camera box" (this is the screw that presses a little metal plate toward the surface)
3) Now, gently, try to remove the camera and place it next to the motherboard.
4) Connect the motherboard with the camera. This was a little tricky, (make sure that it is pluged in correctly)
5) Now take the whole package (that is the motherboard connected with the camera) and place it back in the case, push the camera back in its correct position. Try to get the motherboard to match the screw holes .. It´s a little tricky to get it in exatly but with a little patient (and a little force=) it´s gonna work out.
6) Then it is just to get everything together and hopefully your camera is working as well!