Drivers door has stopped recognising that it is open!

The door light or interior lights no longer turn on when you open the door and the dash light doesnt come on!

Anyone know what could be causing this and is it a cheap or simple fix?

Possibly a microswitch failure in the lock assembly. This could be a switch failure or a dry joint.

When the car door is shut, and locked, does the alarm LED in the door flash or remain on solid?

I have this exact problem.

My LED flashes when locked, but doesn't recognise that the door itself is open...

short fix can be to spray loads of WD40 into the lock mech. I had this issues but in the end swapped in a 2nd had door mech to solve it. You can solder a new micro switch in there and there is a how-to somewhere on here.

It's a common annoying fault.