I've just installed Lightroom 5.7 on an MSI laptop under Windows 8.1.
The "-" key doesn't decrease the grid size, and neither does clicking on the "decrease grid size" field in the "view" menu.
Unfortunately, the "increase grid size" did work and now I'm stuck with just two images in my grid view.
Lightroom 5.7 works perfectly on my desktop under Windows 7.
Yes, thanks - I didn't even know there was a slider on the tool bar, but that at least does work.
The decrease grid size menu item should also work, so I'd like to get it fixed somehow, but at least I've got a useable grid now.