Turn off your phone by pressing the “Power” button and remove your SIM card. The SIM card is usually located on the bottom of the phone or underneath the phone's back cover.
Inspect the SIM card for signs of damage. If you’ve dropped your phone in any way, you may have knocked the SIM card out of alignment. It might be better to have your service provider re-align the card in case you accidentally cause more damage to it.
Insert the SIM card with the gold bands facing down. You may not have inserted the SIM card properly or it may not have been pushed in all the way.
Check to make sure your SIM card is compatible with your phone if you’ve purchased a new SIM card.
Turn the phone back on by pressing “Power.”
Talk to your service provider if you are still experiencing problems. If you’ve recently changed your service providers, you may need to have your SIM card configured. Also, recurring problems could be a sign that your PUK or personal unblocking key was entered incorrectly. Only your service provider can fix these problems.