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Given that you did a hard reset to factory settings, your phone's configuration has been completed wiped. You will have to set up networking for your phone, with your provider, as if it were new out of the box.
I don't know what provider you have for mobile networking, but you will need to go into Settings - Networking - and turn Off "WiFi" and turn On the 2G/3G/4G mobile networking that your phone has capacity for.