Don't detect mobile network

Hello members,

My Samsung S3 I9300 don't detect my network anymore. All I did is reset the phone. I didn't use this phone for a while because I bought a new one. I want to give this phone as a gift to my sister. I replaced sim card holder slot but it still says can't detect network. I also replaced Battery but nothing works. I tried other simcards(didn't work) and did try my simcards on other phones(that works).

Any Suggestion ?

Thanks in advance.

I replaced Samsung Galaxy S3 Antenna. That didn't help !