So on this circuit are two ceiling garage lights, a plug in the ceiling for garage door opener, a porch light, and inside the house, wall plugs in an "office". The garage ceiling lights are on three-way switch set-up. The breaker did not blow. The plugs in the office work. Home was built in 1982 (and in US).
In this junction box the neutrals and grounds are tied together. (Is that supposed to be like that?) There is a black wire tied off to nothing. There is 90 volts between the white/black/black group and the white/ground group.
The failure seemed to occur after some siding work on the house (using two-inch nails) but I cannot be 100% sure - though it was that evening we noticed it. One switch of the three-way ceiling light circuit, the porch light, and porch light switch are in the wall where siding work is taking place. They have the porch light on the outside removed at the moment for the siding work. The office wall sockets have 118v. The switches do use the push-in holes and not the screws to connect the wires.
Is it possible it is a nail hit the wire and would cause these symptoms without blowing the breaker? Why does the office have 118v? The office is between the breaker box and garage. Is it possible bad neutral connections (which I understand can cause voltage drops?