It's none of what you guys have described so far. Literally, you hit the shutter release and mirror goes up, but nothing else happens. The mirror doesn't come back down either. This happens at all shutter speeds including Bulb. The battery is fine (first thing I checked even though it's a mechanical shutter). The shutter curtain won't open. Very weird. It's definitely some sort of mechanical connection between the shutter release and the shutter itself. You can't even wind the film after releasing the shutter.
I'd never admit to anything... haha. Seriously, I don't think it was anything I did because I just fired it a few times and then it happened. I think the guy who owned it before abused it a bit and just sold the camera to someone he knew to be a novice (she is a complete beginner with film; I'll take the credit for converting her from digital). He probably wouldn't be able to get rid of it on eBay because he'd get bad feedback if he didn't admit the problems. You're probably right, it is an old camera and probably needs a CLA deperately.