(Phone) Nokia Lumia cyan "No Sim Card Error" Keeps popping up!

I just bought a Nokia Lumia cyan (phone) from a friend at school. I reset the phone to the factory default settings. And It was working for maybe a day or three. Until now, it keeps popping up with the "No Sim Card Error". It usually only popped at the start. Now it pops up like every 1-5 minutes and after it pops up the second time the power button won't put it to sleep. You have to hold it to shut it down then it just turns back on by itself. Also the internet doesn't work for Cortana or any of the default apps but it works for Clash of The Lords 2.

Please Help I do not want to reset everything again!!!

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