@FRANKIE I had the same problem some months back when mine was off road for the winter, I turned the ignition over every weekend and let it run for a while even when I had the whole centre console stripped out. Then one weekend for some reason I had the same issue as you described - central locking worked fine lights up and nothing - not even click of the starter motor. Looking back on some of the past receipts I had when I bought the car it seems the battery was replaced only a couple of years ago! I took the battery out and put it on trickle charge for best part of the day and it fired up first time when I put it back in. Touch wood its been fine ever since.
I would suggest give the battery a good charge up first to eliminate the simplest potential issues???
Best of luck mate!
Andy