1, mobile phone SIM card and mobile phone card slot shrapnel poor contact, resulting in the SIM card circuit can not work;
2, the mobile phone card may be inserted backwards or in the wrong position, try a few times;
3, the location signal is not good, you can change the place or try again later;
4, the mobile phone SIM card is not registered in the network, at this time you can insert this SIM card into another mobile phone, if no service is also displayed as the reason for the SIM card. 1, to backup the address book, before replacing the mobile phone card, use software or computer backup address book; 2. Untie the bank card and change all the phone numbers; 3. The mobile phone number of various software, QQ, wechat, and even the password of some social networking sites, etc., many software are bound with the mobile phone number, and it is troublesome to change the card without a spare mobile phone; 4, Alipay, all kinds of treasure and online shopping phone need to be changed.