IMHO
step 1) Install the sim card in another cell phone and make some calls

if step 1) is a success goto step 2 else get a new simcard

step 2) make sure the firmware image being flashed is the correct one for your region and is the latest version, for e.g. the correct file name for US is ''RX-51_2009SE_3.2010.02-8_PR_COMBINED_MR0_ARM''

step 3) flash the latest and correct image for your cell phone using the command line flasher too.