It's possible that the cam popped loose (or isn't there) or isn't seated properly.
That would cause that problem. Check underneath the rangefinder housing, there should be a metal flap on the inside top of the body. There should be a spring and a pin, with a metal 'cam' in the middle.. If you push the pin, the rangefinder image should move..
Hope that atleast gets you started in the right direction.
Whatever you do, don't mess with the inside of the rangefinder yet.
Don't touch the mirrors, the half-silvered one is ridiculously fragile. If you touch it, you stand a great chance of wiping the coating off and turning it into a clear piece of glass