Heloo DannyPhantom,
Often people wire receptacle outlets with two conductors under one terminal screw. After some time (days to years), one wire loosens and comes off. Downstream, all receptacles will be de-energized. This is common.
And, if people install the receptacle outlets with the spring loaded push-in wire terminals, one could have come loose over time and burned off. Those devices should be avoided. This is common.
Other times, people will use a twist on wire connector (like a Wire Nut) in a receptacle box. After time, one wire can come out of the wire connector, de-energizing the downstream devices. (Not terribly common, but happens)
And, if the building was wired with aluminum, people very often don't know that a standard receptacle outlet used with aluminum conductors will oxidize or the terminal will come loose from normal warming-cooling cycles. A conductor will come off.
How To Fix-
You will have to do detective work and try to figure out the first receptacle outlet on the list. After turning off the circuit & verifying it is off, remove the receptacle and look if a wire came off.
Often it is not easy to figure out the upstream device, so you may have to do random checks on many receptacles- Always With The Power Off.
I hope this helps,
Paul
