When I highlight a combo box, the default hotkeys should be alt+down or f4 to drop the menu down.
The issue I'm having is that while alt+down works, f4 does not. I just got a new computer in my office, and f4 worked on the old one.
My keyboard does not have a f-lock key on it. That seems to be the internet's general response to my problem, but that doesn't work.