This was my first "real" camera and lens combo. Took a lot of great photos w/ it. You don't have to cock the shutters on any Canon camera to mount a lens, at least to my knowledge. FD lenses are funny about how their apertures work though. I don't remember the details, but if you go to google and search for a fix (there's something that needs to be set on the back of the lenses, that I remember) you should see it. Make sure that Rube Goldberg little sliding lever on the front of the camera near the bottom of the lens mount on the left side isn't pushed in and engaged too, as that will cause problems like you're having. The lever allows you to stop the lens down, but it was so fiddeley that I never used it.
Try this