Why can't I assign function to the windows key? ZorinOS

So I'm on ZorinOS, and I go to

Zorin Appearance > Interface >

And in that Menu is the option ""Left Super Key".

I've been led to believe that's where I assign the action of the windows key. Except it's greyed out.

I'd like it to do exactly what it does on WindowsXP and Windows 7, where a start menu pops up.

At one time it did that. Then now it's a totally different action that I can't quite explain. It's like it shows every single open app in a zoomed out view, and you can click one to zoom in on that window. I know, my description sucks.

But I can't select Left Super Key, and I don't know linux well enough to know why.