Welcome to the forum!
And so the problem is that the shortcut for turning on the grid doesn't work? That's one of the few key shortcuts I use, so I know it's Shift + 3 (or the number sign), unless you changed it? Could you have customized that shortcut previously? If you don't remember, you can double-check in Inkscape Preferences > Interface > Keyboard Shortcuts.
Of course, you have to have a grid enabled, in Document Properties, or else there's no grid to enable. There should be a rectangular grid by default, unless you previously disabled it? Check in Document Properties > Grids tab, and make sure there's a grid enabled. Oh, and check that there's both an enabled and visible grid, since it's possible to set them not to be visible.
I suppose it's possible to have made the grid lines so transparent that you can't see them, or you could have switched it to dots instead of grid lines. Those are both set in Document Properties too.
Oh, or possibly there's a custom document in play for this problem? Either you usually use a custom template but you weren't testing with it, or vice versa?
Does any of that help?
