Did this by chance happen to start after you had used a dual
monitor configuration? Folks around here are probably thinking I
believe that's the cause of every problem, but in some cases, we
have found that disappearing dialogs and "freezes" are actually
caused by going from dual monitors to one monitor, and dialogs are
appearing off-screen (which then makes RH look like it's inactive
and not working).
One experiment you can try with either "freeze" that you've
listed is to hit the Esc key and see if RH livens up again. If
there is a dialog open, Esc closes it and returns you to RH.
Just a thought,
Ben