Why is my windows Lumia 521 showing sim missing/invalid?

[Windows Central Question]

since many days my Lumia 521 is showing " Sim invalid/missing .Emergency calls only "
can anyone help me wat should i do to get back phone to normal ?

 

[RichardBurt]

Put a SIM card in it?

Try taking your SIM out and putting it back in. Switch off the phone before doing this.

 

[bmetelsky]

I would suggest that you check the SIM to make sure it is positioned correctly in the holder.

 

[RumoredNow]

SIM cards can and do go bad... If it isn't working after the above talk to your carrier.

 

[ramyZgHR]

Is your Lumia new? I had the same problem when I bought 925. After half an hour of checking my sim, I connected phone to wifi and updated my software. I don't know why, but that helped.