I can not connect to the GSM network and 3G

Hello, I have a cell Z3 model d6653, bought by eBay in November, he ran smoothly until February, which is not connected to any network, or GSM or 3G. I could verify it is that the cell is in constant "airplane mode", in which the previous system KitKat it could change, now leaves me with Version 5.

Does anyone know how to fix this problem or make effective the guarantee?

Cheers