Okay, two-cents time: There have been great suggestions, including the extension cord reference idea, which I've recommended many times, but I use a solenoid tester instead of a bulb. You can wire-nut wire to the probes if you need more length.
Added: It can indeed be handy to know whether the problem in a broken hot or neutral (I know, I know), or both.
Wire rarely goes bad in the middle of a run, but if someone modified thne house, such as adding a doorway (look for mis-matched trim), they may well have buried poor splices. The wire-tracer idea is the gold here.
If the receptacles and/or light are working now, that's great. Plug in a light or turn on the ceiling light (or both) and start wiggling stuff. The lights will flicker. You might not even have to remove the device to find a loose connection.
If they're out again, what you might try with a tracer like the afore-mentioned Amprobe is to de-energize the working section and inject into the dead part. Don't forget to look in other rooms.
By the way, if every receptacle has a single cable (other than a circuit extension), they most likely spider from the ceiling box. If they mostly have two, then don't forget to look in receptacle boxes in adjacent rooms, back-to-back.
Also, a lot of older wiring methods (K&T, BX (etc.), and early NM) used soldering and taping, sometimes not inside boxes, and these joints can break if moved much (and you may not have been the first one to mess with them.)
As for back-feeding, if done temporarily, as a tool, yes. If done as a fix, it's imperative to supply from the same circuit, unless you find and terminate both sides of the break (but then, if you found it, just fix it.)
Points to remember when troubleshooting existing installations (and please forgive any seemingly redundant or elementary info):
1. The system worked at some point; something has changed. You have to find out what and where, and restore it.
2. Human installation is infinitely more likely to be the issue than manufacturing, so suspect connections first, devices second.
3. The problem is at either end of a piece of cable*. It can be in the last working box as well as the first non-working one.
*Barring in-wall cable damage.
4. Many older homes were wired up-and-downThey'd start the home run at, say, a living-room receptacle box, run up through the floor to an upstairs bedroom, across the the other wall for one (or maybe in the next room) and back down to a kitchen receptacle.*
*Before those rules, of course.
