hi newbie here i bought a wrx 2003 blobeye without ecu as previous owner had a standalone and sold it. now heres the problem i have bought a ecu with keys etc but car wont spark its turning over and immobiliser light comes off soo im dumbstruck on what to do can anyone help? and to add to the mayhem when diagnostic is plugged in it doesn't read anything

 

Sounds like the computer is 'dead'. With key on, look for a 5 volt reference (easiest to find on the throttle position sensor). i.e one of the wires going to TPS should have 5 volts on it. If no 5v reference then computer not alive. Next step would be to check the powers and grounds going to computer (you will need a wiring diagram).
This video will give you the testing procedures:

 

Thanks mate I'll look at it tmr but to be honest I dont know much about the electrical side of things so gonna call auto electrician