I've used this forum a lot in the past to troubleshoot/fix issues with my RRS's in the past so thought I would share a recent experience for others.
I went out to my car (2013 Range Rover Sport L320) last night and the keyless entry wouldnt work. No response when I touched the handle, I then tried open the car with the keyfob, no response. I replaced the battery in my keyfob and still no response, I went and got my additional spare keyfob, no response - hmmmmmmm.
I gained entry to the vehicle using the emergency method, central locking wasnt working, ignition wouldnt engage, couldnt turn on any of the lights etc so this lead me to believe it was an issue with a dead battery. I hooked up the cars battery to my other vehicle and still no response.
I went through every fuse in the engine compartment and all relevant fuses in the passenger compartment.
I searched google, went through forum posts etc and still nothing, after 2 hours of troubleshooting I gave up the ghost and tried to get a call out from Land Rover assist - they arranged for someone but when I found out it wasn't going to be a Land Rover specialist I called to complain and eventually they cancelled the call out and I got a refund.
This morning I thought I would do one last search for the answer and came across a person with a different problem who's fix was to disconnect the battery "to reset the system", so I tried this and viola the car has sprung back into life and is now working as expected.
I'm not too sure why I didn't think of this last night and I can't say what the root cause was but I have saved myself ~£180 in a call out charge and that makes me happy!
So, if you have a Range Rover and ever get a scenario as described above - car not responding to key fob and unable to engage ignition or other electrics then try disconnecting the battery for ~10 mins to reset the system.
I shall now be keeping an appropriate sized spanner in the care in case this happens again and I'm not at home!