I cant use the Z command for wireframe I was doing some 3d modeling from a tutorial then when I added a circle I pressed f8 instead of f6 then after that z won't toggle wireframe. What did f8 do? Ctrl z works but didn't undo what ever f8 did.
To get "Z" to toggle wireframe again, turn Object > Display > Maximum Draw Type to Texture or Solid if it is currently set to Wire 



Or for the animated version from user Timaroberts



Sources:Can't get my model out of wireframe mode, GIF from Have I toggled wireframe?