My Nikon FG arrived today but it seems to be "stuck"....like the mirrors locked up or something. I can't see though the viewfinder. I can't advance the film and when I press the shutter nothing happens. I replaced the battery (and tested it) so I don't think that's it. The lens comes seats and comes off properly. Thoughts? My gut feel is it isn't broken but something, most likely the mirror is "stuck" or locked up.