1: Confirm whether it is a SIM card problem. Restart the phone and re-insert the card. After all these steps are useless, find the phone to confirm whether the SIM card is broken. If there is still no response on other mobile phones, the card is broken and needs to be reissued.

2. Restore the factory settings, the mobile phone can't read the SIM card, and there is something wrong with the baseband (a BIOS dedicated to communication). You can try to restore the factory settings and back up first, such as address book, SMS, photos, etc. After the backup, you can go to the setting center to restore the factory settings.

3. mobile phone brushing machine,

The method is as follows:

Step 1: Back up the important information of the mobile phone.

Step 2, download and install the latest version of itunes software on your computer, and open itunes after installation.

The third step is to connect the iPhone to the computer with the data cable, and you will hear the prompt that the computer has been connected successfully.

Step 4: Please turn off the iPhone first, and you will hear the prompt that the computer connection is unsuccessful.

Step 5: Please press and hold the ON/OFF key and the home key at the same time until the first 10 second. Please immediately release the ON/OFF key and keep pressing and holding the home key.

Step 6: At this time, iTunes will automatically start and prompt for recovery mode (iPhone will always be black). Then you can press and hold the shift key on the keyboard, click "Restore" and select the corresponding firmware to restore.