Can you please post a screenshot of your Presets panel?
Here is a screenshot. (sorry, dont know how to only make a screenshot of that specific part).
As you can see the presets I bought are not showing at all, I followed the whole process how to install them several times but they just stay in the develop folder. The pre installed ones do not do anything either as mentioned before.
Your screenshot shows that the folders of presets are all collapsed -- clicking on a folder name does nothing. Click on the triangle next to a folder name (e.g. "Vignetting") to expand the folder and see the actual presets inside it. (LR 7.3 now calls these folders "groups".)
It's not very good user-interface design, and lots of users get tripped up by this.
Thank you so much John!
I feel a bit stupid spending so many hours the last weeks trying to solve this..
No need to feel stupid. It's a poor UI design -- while Mac users might be familiar with the triangle idiom from the Mac Finder, it's not common on Windows. Further, the folders should expand/collapse when you click on them, not just the triangles.