Samsung Galaxy S2 — My GT-9100 is dying... HELP!!!

Hi,

I'm desperate, my English as my knowledge of android are not very good, so i'll do my best

I hope someone can help me!

I have a gsII GT-I9100, it was from my friend and, as I know, it was rooted or flashed to Jelly bean about a year ago,...

A few weeks ago, I had problems with the mic and took it to the technician, he changed the flex and everything worked fine the first day... then started having problems with the signal and a "no network available" error.

I researched online and saw something about IMEI, i checked on my phone and had the original IMEI.

Last week I had no signal at all, my sim is not recognized, and now my IMEI is null...

I decided to go to the technicians and he told me that he can fix it... but when i back he said that he couldn't mount it as usb and that my new flex was burned, i went to my home and put the original piece and I tried to conteccting it to my pc, but doesn't recognize it... I realized that my phone doesn't show the "usb symbol" at the status bar....

Now I can not try to fix it... help me!!

Oh.. and my friend told me that he doesn't have a backup (he mentioned an efs file or something like that..?)

Thanks...