Urgently Need Help Diagnosing Dead Electrical System

So, once you get to the white wire terminal strip, check with your meter from there to C. If you have voltage, then the power has run out the hot wires, through the lights and fans, and come back to the neutral terminal strip... But it can't get out from there back to C which connects to your battery.

If you find this is indeed the case, put a heavy duty jumper wire from the neutral strip back to C and you should have your devices working again.