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Make sure that the network mode is set WCDMA/GSM under settings > more > mobile network > network mode. Also try to search for network under network operator that you find under the same menu as network mode.
Turn of your phone and remove the SIM card for a while. Put it back and see if you get any connection to the network.
If you still experience the same behavior I would suggest that you try with another SIM card in your phone.
