My LG G3 S NETWORK CONNECTION PROBLEM

[nahian7]

As the title says my phone keeps saying mobile network unavailable until insert valid SIM card and restart my phone. Then I got connection for 5-8 seconds. Then It counts up to 10 on the screen show this text(Sim card removed
The mobile network will be inaccessible until you resume using a valid SIM card inserted) and shuts down and then starts up again and says no SIM card inserted. my SIM card works in other phone. its happened again and again what can I do?