A contractor who is not an electrician tried to be "helpful" and opened an outlet box (and other nearby boxes that were drawing the same power) that wasn't working to try and fix it. He changed some connections, added a wire, and also cut a wire. He ended up getting power to the broken outlet, however his "fix" ended up blowing a different circuit and we lost power in an adjoining room. I had a real electrician come in - he said the contractor had added an unnecessary wire which he removed, and he also said the contractor had connected a ground and Hotwire. (He said they were the same color so it may have been confusing). So now all of the outlets, at least in the two rooms that were seemingly effected, are working and the fuses are fine. He can't figure out what the cut wire goes to so he just capped it off. he said there was no danger from having this cut wire in the wall - he said since my walls are concrete I won't have an electrical Fire even if that wire did overheat. He said if it was resting a short somewhere then a fuse would blow. He said since it appears everything is working now it is hard to figure out what that wire was for. Does this all sound right and I should just not worry about it? Or do I need to start tearing down walls to figure out where the cut wire came from?
Does this all sound right and I should just not worry about it?
If it is causing you concern, you could pay another electrician for a second opinion. I wouldn't bother but you may feel it worthwhile.
do I need to start tearing down walls to figure out where the cut wire came from?
If you must know where the wire leads to, that might eventually be necessary.
There are other tools that can be used for tracing wires without requiring opening up the walls - for example, tone-generators are often used on telecom wiring, I imagine you could isolate the power supply to the house and use that kind of tool.
This might be a lot of work for little reward.
A disconnected wire is unlikely to pose a hazard unless it is a ground/earth wire which might mean that some light-fitting or power outlet which shoudl be earthed is not. An electrician can test lights etc to test the earthing arrangements meet code. You can buy relatively inexpensive tools to test outlets - these might give you some reassurance.
If the electrician has pronounced it safe and has capped off the wire, I would leave it at that unless you have good reason to mistrust the electrician.