Why my phon no have signal?

Make sure the SIM card is not blocked or forfeited. If it is still active, it can and it doesn't appear. You can also back up your personal data and delete your Google account.
Open the Settings app.
Scroll to and tap General management.
Tap Reset.
Select Factory data reset from the given options.
Read the information then tap Reset to continue.
Tap Delete All to confirm the action.