1. Check the signal strength on the phone screen. To increase signal strength, move around, or if you are calling from inside a building move closer to a window.
  2. Make sure your phone's profile is not set to silent, flight, offline, or any other profile where ringing is silenced: Select Settings > Profiles.
  3. Check the settings of your active profile, especially ringtone, incoming call alert, and ringing volume.
  4. Make sure that call forwarding is not switched on: Select Settings > Call > Call forwarding.

If the problem persists, remove the battery, replace it, and switch your phone on.