Hi Augustin,
Thank you for posting on Microsoft Communities.
I will be glad to help you with the issue you have with the phone. I understand the frustration when things don't work the way it should.
Please answer the following for us to assist you better:
- Did you make any changes to the phone prior to the issue?
- Which was the latest built installed on the phone?
I suggest you to follow the below link and check if it works.
http://windows.microsoft.com/en-us/windows-10/restart-my-phone
Please reply with the results, we will be glad to help you further.
Thank you.