i need help with a 94 jeep grand cherokee?

i own a jeep grand cherokee , i need help with it badly . i had the engine changed and transmission as well ,when i bought it it had no tranny ,and with no-one knowing about the engine i just got both together . now with everthing put in place . i had a friend with a computer/scanner come by to chk out why it would not start . reason being i have no fire to nothing ; nothing.. when he hooked it up to the plug for ecm/pcu the thingy which tells the scanner wats wrong it doesnt tell the scanner anything its like it was dead as well, so i got another that i knew was good from a salvage yard the guy started the jeep up , okay so i bought it and i replaced it , had my friend come back over with toll and still the same response happens , no communication between the 2...it has fuel, air , oil , and coolant..everything is hooked up . i have chked all links and relays and fuses nothing out of the ordinary is wrong .......CAN SUMONE PLEASE HELP ME OUT........thank you