Right half of my monitor just went black

And if the menu shows across the whole screen fine, it's the other way round - the panel is ok and the problem is upstream. Try a different cable and port first, then plug in another device if you've got a console or laptop handy. That narrows it down in five minutes.

If the monitor's own menu gets cut off too, it's the monitor. That menu is drawn by the screen itself, so a PC, cable or driver fault can't hide half of it. Usually the panel or the T-con board, occasionally a loose ribbon inside. Under warranty, send it back. Out of warranty a repair often costs close to a new one.