2001 Chevrolet Express Computer not talkin

I have a 2001 Chevy express van The motor was bad when I bought it I put a good 5.7 350 in it out of a 1997 z 71 when I got it in and ready to start . There isn't any spark. The fuel pump doesn't work and all the guarded are acting funny. We code tested the computer and it's not talking to tell the motor what to do. The fuse box has power and the relays. I have no spark, no fuel pump, and my gauges are acting weird. The van has a security system or anti theatf thing on it . The computer is not communicating anything what is going on???