[tsac]

If the phone does not see any cell service then it may be defective.
So if you are sure you have service on the SIM and if possible you tested it in another phone. the only other thing you can try is the options settings and make sure the service is not off

options, network connections, mobile network, check to see if the mobile network show a listing. if not then either the phone is defective or the SIM is after testing to be sure it works.

Now if your not talking about the cell service and are really talking about WIFI then the next thing to check is to be sure the service is on also.
Options, network and connections, wifi network.