We would assume that the kazoo you're trying to play can be played by others? Or that you cannot play the same other kazoo that works for someone else? Either case would eliminate problems with the instrument, and imply that it's only your own lack of kazootiness that's the problem.

An instruction that has worked for a few others similarly challenged:

1. With your mouth SHUT hum, a note or a tune. Obviously the sound will come out of your nose, but there likely will be little sense that there's any air going out at all. You can demonstrate that there is a very small flow of air since when you pinch your nose shut you cannot hum with your mouth shut.

2. Continue to hum exactly as before, but open your mouth slightly. You'll probably note that the sound gets a little louder, since some of it is now coming out of your mouth - which probably is a little larger hole in your head than your nose.

3. Resume humming with your mouth SHUT and bring the kazoo - either end, up against your lips. Relax the lips enough to slide the kazoo between them with out changing that you're humming "through your nose."

4. Note that you do not Blow, Suck, Breathe, or in any other way attempt to move air through the kazoo. The ONLY thing that's really supposed to enter it is the SOUND of your humming. There will unavaidably be a small bit of "flow" along with the sound, but it's entirely incidental, unnecessary, and actually a bit undesirable.

(It's traditional to use "Grandfather's Clock" as the tune one hums to demonstrate.)

John