Dear Bob:
Just to add (probably unecessarily!) to Gunny's perfectly correct answer:
Don't try to hit both keys at "exactly" the same time! You need to hold the
Control key down, and then, while holding the control key down, tap on the
";".
As a teacher, over the years, I've seen so many students desperately trying
to hit both keys at exactly the same time, I've developed the habit of
describing the keystroke in this way!
HTH
Fred Boer