Bad Receptacle or Something Worse?

I suddenly started experiencing some issues with a set of outlets not working, they would go off and come on randomly for a few hours, then they went out completely. There are a total, I believe, of 4 receptacles, 1 switch and 1 light (the light and one receptacle are on a switch by the door). The problem seems to start at the door around the switch, because the light and receptacle controlled by the switch and the receptacle by the switch are not working. Using my digital voltmeter set to 200A, I was pulling 120v from both (black and white) wires to the (uninsulated) ground the black wire to the white wire get 0v, this was with the switch was in the off position, when I put the switch in the on position the white wires stated 120v and the black dropped to 80v; still 0 between black to white. I replaced the switch, same result. I get the same results on the non-working receptacle connected to the switch. The non-working receptacle not on the switch pulls 120v from all wires to ground regardless of switch position, but gets 0v from black to white wires. It's probably worth noting that the ground wires were disconnected from both the switch and the switch controlled receptacle; but the problem just started and they appeared to have been disconnected for quite a while. The house is about 40 years old, and there are no GFI/GCFI that I'm aware of on this breaker. What would cause the problem and how do I fix it? Thanks, Justin