need help with galaxy s 3 please topic

my nephew rooted my phone (little turd) I thought I bought it that way. so.... the phone updated on its own and when i woke up it was stuck on att logo, I reset phone, battery out,and hard reset nada nothing, so I sent it to shop not at&t seems how where I live it would take 5months to get there and back not to mention no warranty seems how he messed with it. The guy flashed it and got it working but when I got it back it says no sim please insert the sim is good, I downloaded phone info, i read it on this site and there is no baseband,imei,modem board can anyone please help me please I have a decent understanding of computers and software I need proper direction thank you so much in advance

from lawrence in kodiak alaska