Nikon FG suddenly stopped working--not bat...

My 30-year-old Nikon FG suddenly ceased working on Friday. Film wouldn't advance, mirror wouldn't close, and, though the film rewound (I thought best to get it out) and the button pressed to open the camera back, the button would not pop back out when back closed; and when I tried putting in a new role of film, I could not advance the spool to put it in. I tried new batteries and also cleaned the connecting plates/tabs that the batteries touch, which I thought would solve this, but it made no difference. Camera has worked for decades--only problem previously is that, for the past five years, the film counter starts at 14 instead of 1. Help!