Replacing the engine should i replace including all the wire sistem and computer too or with out it?

i mily name is julio im sending this message
from ogden Utah.  The reason why its
because i buyed a 2001 BMW 325i that i had
a problem with the transmission so i buyed
another one same model but 2002 325i. So i
put my engine on the one i buy last with
everything including the computers and
cables stuff in the engine the car acts
normal when you are about to start it but
when you turn the key on sounds like its
going but it wont stay on not matter how
long you hold the key turning it on it wont
run. I used to see a signal by the light that
tell you that you are in parking reverse or
drive there was a little sircul with something
inside telling me that the. transmission was
with damage or something i think.  So when
i turn this other one that i just put the engine
and everything else computers too though
so when i turn the key on just to where the
radio and all the light turn on for a while until
all the light in the cluster by the steering
wheel some light turn off but that one by the
parking or driving letters are in the clusterI
was just wondering if you could of give me
any idea what should i try to make it work
please i will appreciate any idea you might
have that it don't even cross my mind right
now thank you and have a great night or day
there where you are