All objects are just black lines in 3D view? I was quickly changing some text and not sure what button I accidentally clicked which caused this to happen, pressed CrtlZ multiple times but nothing helped. Is there a way I can revert this back?
You are looking at the "Bounding Box" shading mode.

Simply press Z twice and it will return back to the normal "Solid" shaded view.
Or you could just click on the Viewport Shading button in the 3D view's header, and then choose "Solid".