If you have no imei ussaly it is baseband related so check the BB PMU otherwise reball the BB CPU if this wont work you need to swap the under ( RF ) board you will need to put the original Wifi IC, BB CPU and Eeprom on an new working underboard most of the times i will just swap the underboard because it saves time and they arent that expensive if you have imei and cant activate its ussaly WTR related some of the times it could be the chargeflex and dont forget to flash the device after repair otherwise it wont work