It is a new handset. It opened with the 4 digit PIN many times during the day. When it asked me to restart after I installed a SIM, I switched off the handset and switched it on. It asked for the PIN and I entered the correct PIN. Neither did it reject nor did it restart. Many times I tried this landing on the same status. I need help how to go about it.
Welcome to AndroidCentral

Thanks for the question. Hopefully we can get you sorted.
To restart your phone, just hold down the power button for 2 seconds. A menu will pop up that gives you the option to Restart or Shutdown.
There shouldn't be a need to enter any PIN or password when restarting the phone. Only once the phone has booted up, you should be prompted to enter various passwords (if set)
Does this help? Hopefully I've understood what you were talking about.