The only suggestion I can think of is to work back through all your steps.
Also, it's worth putting a multi meter across the battery, a small 12 volt test light will work fine on an all but really dead battery, but when you load it up with the headlights, fuel pump and ECU it may be dead enough to not make any sign of starting.
Check all the other relays etc and recheck anything that you may have had to undo in the process.
Rest assured, it will be simple, and you'll kick yourself when you see what it is...
Mick
