When I try to turn the knob to tighten the snares, nothing happens. How do I fix this?

The snare tension knob is probably tightened as far as it will go. To correct this, turn the strainer to the "off" position and loosen the strainer knob until the slider, the part that goes up and down, is halfway. Loosen the screws that hold the plastic strap or cords on the slider and pull the strap or cords about an eight of an inch. Retighten the screws. Turn the strainer "on" and test. Readjust if necessary. For best snare sound, the snares should be centered evenly and squared on the snare head.