First things first: Does the key turn in the lock? If it turns does it have any effect? If the lock itself doesn't work, then you need to open it up and figure out what is broken or rusted. It's pretty common for the mechanism to get rusty and need an overhaul and lube.
I'm assuming from your description that you can't hear anything back there when you actuate the lock. If you can, then you know it's mechanical not electrical. If you can't you should probably start by ensuring that the switch is passing current (using test light or meter). Assuming it is, then you'll have to open up the panel and see if it's reaching the hatch. If it is, then the problem is the solenoid. If it isn't, then it's somewhere in the wiring between switch and hatch.
Either way, you'll probably need to take the panel off.