Nissan Almera Sport won't start?

I have a Nissan Almera Sport on a Y reg plate,,,
I've had the car for 5 years & it's a good little runner apart from today that is!!!,,
I pressed the unlock button on key fob & I didn't hear the "clunk" sound it makes as it automatically unlocks??, so I unlocked it by putting key into door handle & alarm didn't go off????
When trying to start engine nothing happened, I turned key & it was completely silent & dead, it didn't even make the draining sound as if it has a flat battery & just needs jump starting. When turning key all lights came on the dashboard but no sound & no engine ticking over - nothing at all!!!!!
I took key out & tried pressing the unlock part on key fob (whilst sat in car) & not even the passenger door would unlock.. I tried to unlock the passenger door manually from the inside & I can' even do that??
Is this something to do with the NATS code on key fob or some kind of electrical fault??