Default I9100G mobile network not available

Hello All

i have dropped my galaxy s2 i1900G , and broke my screen

i took it to someone to repair it , he replaced the screen and replaced the board as he said

now i cannot connect to the network , when try to call it says ( mobile network not available )

when i try to search for network it says ( error while searching for networks )

i have tried to flash stock roms many times , and tried wipe many times

my IMEI and the baseband are still there , i havent lost the IMEI and baseband

i have tried to flash a modem , but the same error

please help