ECU issues

[deesvtsT]

when my rev counter packed up i traced it to a broken wire in the front under bonnet wireing loom, i had a s reg vts that i was breaking so i put the loom in and all was well, but since my ecu had a idle issues i thought to change the ecu. so i did ,I also changed the transponder ring and key . but now it wont run and the key light is flashing ,
Is there something ive missed
or something i havent changed
can anyone help:wall: