Can't turn on the shower

[brintage]

Unfortunately, the title explains it.

I moved into a new flat a few days ago and spent about half an hour trying to make that thing work. I pulled, pushed, twisted, however, nothing worked. Also, I found this website a few minutes ago and must admit that I know close to nothing about showers so please excuse me if this is really dumb.

 

[ImOld]

Looks like the typical pull-up diverter. Are you getting water to the tub? Does it, the brass part, move up and down? If not, it is probably corroded in place. If so, unscrew the hose underneath and see if the water is getting that far.