My sony xperia m2 says 'no sim card no service' even though i have restarted it numerous time, but i don't know if it is my Sim card is the problem or my phone. And if it is the Sim card will i need a new one?
If it is a faulty SIM it would need to be replaced.
Could be bad contacts if it has been in a while. Take it out and rub the SIM with a pencil rubber and try again.
If you could try it in another phone, so much the better.