You may be experiencing any of these issues:

• No signal bar on the signal indicator of the screen
• Unable to send and receive messages
• Unable to send or receive calls
• Unable to use mobile data

The SIM card may not be recognized by the phone, or may have been positioned incorrectly in the phone. Follow these steps to validate the SIM card:

1. Check that the phone is recognizing the SIM card.
2. Look in the upper right hand corner of the device where the signal bars are displayed:
   If you see one or more signal bars, the phone is receiving signal and reading the SIM card. See My cell phone network connection is unstable for more information on improving your signal.
   If you see a No SIM message, the phone is not recognizing the SIM card. See I can't activate my SIM card for more information on inserting the SIM card correctly into the phone, which may address the issue.

Your phone may have lost its connection with the network. Follow these steps to refresh the connection:

1. Navigate to Settings > Airplane Mode and toggle the mode On and Off.
2. Check if the network is 3G or 4G. This can affect network signal quality and speed.

Some issues can be resolved by power cycling your phone. Follow these steps:

1. Press and hold POWER until the Phone Options appear.
2. Select Power Off and wait for the phone to fully turn off.
3. Wait for a few moments, and then power the phone on by pressing and holding the POWER button.
   This will allow the SIM to forget the previous connection and find a stronger signal.

Safe Mode prevents third-party applications from functioning and is useful when troubleshooting issues caused by installed apps or services. See How to boot into Safe Mode to check if signal quality improves.