Sorry to hear that you have issues with your phone.
There could be several reasons for an issue like this so i'm afraid it's hard to say for sure what's wrong with your phone.
I recommend that you first try your phone in safe mode to make sure the issue is not caused by a downloaded app.
If the issue remains in safe mode i recommend that you check so that your SIM card is inserted properly and that you also try the phone with another SIM. If you have an SD card, also try your phone without it.
