No Signal on Phone or SIM Card Not Recognised

The cause is often a loose SIM contact, an outdated network configuration, or a software freeze. Steps: 1) Turn the phone off, remove the SIM card, wait briefly, then reinsert it. 2) Restart the phone. 3) Go to Settings → Connections → Mobile Network and manually search for and select your network operator. 4) Reset network settings (Settings → General Management → Reset → Reset Network Settings). If the SIM is physically damaged or very old, a free replacement from your provider is worth requesting.