Just in case this saves someone else (or future me) some head-scratching.
Work issued me a new laptop, onto which I promptly installed ST3. When I first hit ctrl-alt-down arrow to go into column select mode my display turned upside down. I've seen this dozens of timesby now--this is the graphics card add-on program making it easy to rotate my display (though why 180 degrees is a useful rotation that they want to serve is unclear). I hit ctrl-alt-up arrow to put things back to rights, and then go into the system area to look for the (in my case Intel) icon to turn off its hot-keys.
But now I go back into ST3 and those key combos don't work at all. Display stays properly oriented, but my sublime cursor moves noplace.
Is ST3 even receiving those keypresses? I open its console with ctrl-` and type "sublime.log_input(True)" to turn on key event logging. Nada, zip, nothing--something is completely eating those keypreses. I google for a bit (mostly finding posts from people who have inadvertently rotated their displays and don't know how to un-rotate them) and didn't find anything useful.
So I pull up the full Intel HD Graphics Control Panel app and go into the hotkeys section:
I enabled hot-keys & tried sublime again. That worked. Then I disabled hot-keys and it still worked. So I'm calling it a fix. This seems like a bug in Intel's utility though--it seems to be eating keystrokes that it's been told to ignore.