Hi Andy.
Andy and all of these it could be.
logically one at a time tick them off, but not necessarily in this order.
fuse box - not completed ignition circuit
key fob battery dead - not sending a signal to ECU. the sensor is in the plastic ring around the key hole
you've alarmed it unbeknown to you.
steering lock - seriously, it happens!
youtube has loads of vidoes of various people doing push and hold sequences on your key. It'll be a combination of that and holding the buttons in whilst turning etc.
try also putting it in N and then turning the key...
good luck.