Why am I not receiving network signals on a Samsung S3 T-999? I just bought a Samsung S3 T-999. The problem is when I switch the cellphone on, it connects to my network but just for a second. The moment that second is gone, I lose signal completely.  So it's not like the IMEI is corrupted or something. Moreover, the phone is not asking for an unlock code at all, so I assume it is unlocked too. 

What could possibly be the problem? How can I solve it?

This is the screenshot:
It was a really stupid thing. My phone's network mode was set to cdma while my country operates in gsm. It solved it.