disco 3 none start

Hi guys. Fitted a new high pressure fuel pump belt to my disco today. In order to do it had to take the battery, battery tray out and disconnect all the wiring behind the battery to give me extra access to the belt. Having done the job and rebuilt making sure everything went back in the correct order, it now wont start! I cant for the life of me understand why? Any help much appreciated chaps

Total utter guess from random stuff I've read on LZ - has the key lost synch with the car etc?

Sit in the car. Lock then unlock on the key a couple of times and then try and start it