I am a very young collector starting out, and just recently bought a 1912 Hamilton 17J 924 from a antique mall. It worked for about 3 weeks with no issues. One day I came home and it stopped. I gently shook it back and forth to see if it would start, but it didn't. When I shook it, I could hear the pallets hitting the escape wheel, but the second hand was not moving. I tried winding it, but it is already fully wound, and won't budge. I can say that it is at LEAST not a balance staff issue, because I checked that. I think it is a mainspring issue, but I am not sure. I have done some research, but that was inconclusive, as I could not find another watch with the same symptoms. I need to know what the problem is, but I am very young and do not trust myself to take it apart. I want to know the problem so i can estimate a repair cost, as I do not have a job, or any source of income.
This is my first post, so please excuse any spelling errors or any misused technical terms.