I have somehow managed to show all guide lines. How do I hide them?
you can change that in Styles. You can also change it under the view menu, and if you want to make it permanent, update or save a new style.
Or create a layer for guides, and assign the guides to this layer. Then switch on / off this layer as needed.
Or use FredoGuides to toggle their visibility (and optionally their color), which can be saved by scene.