It is the Pro-S.

I've tried it with the back and lens off. I've tried it with the red dot showing and not. The mirror appears to be all the way down. No matter what I try the mirror doesn't budge.

I just tried it with the film back and lens on. Red dot by film winding lever showing. Dark slide out. shutter button on white dot. Not only does the mirror not go up but also it doesn't make the shutter release. It's almost like the shutter is disengaged??