110530-2230 EDT
pridelion:
You have lots of good suggestions. I will suggest another which also uses an extension cord.
Use a 3 wire extension cord connected to a known good circuit near the main panel. This should provide a good EGC, neutral, and hot line. Use three test instruments --- a good DVM like a Fluke 27, a 25 W bulb with leads to allow connection with any pair of the five wires you have, 3 from the extension cord, and the two in your circuit under test, and last a 1500 W heater, may not need it initially.
Disconnect any loads from all non-functioning receptacles, and bulbs from lights on the non-working circuit.
You can first see if the neutrals seem to be OK. Use the 25 W bulb between the extension cord hot wire and the neutral to be tested. See if any appear to be bad.
Next use the voltmeter between the extension cord neutral or EGC and the hot terminal to be tested. Note: all loads from the circuit have been removed so the hot wire should not load the circuit.
If there is some high resistance connection between the good part of the circuit and the bad part then you may see enough voltage on the bad part to then allow you to find the breaker. There could be capacitive coupling from some other circuit. A real substantial break in the circuit may not provide much leakage current. If this leads you to a single breaker that really seems to control the circuit, then find the last good outlet on that circuit.
Open that outlet and see if there is an indicated problem at this point. The voltmeter may be useful here to check the input and output. If this is the point of the problem, then moving the output wire may make a voltage change of the failed part of the circuit.
If nothing bad appears here then the physical location may lead you to the closest non-working outlet.
Once you get the circuit working again. then use the heater to apply a load on various receptacles and check for excessive voltage drop.
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