how can i fix my dyson dc24 vacuum cleaner?

Its not the switch; it never is.

First try resetting it. Press the red button on the side of the brush roll a few times. If that doesn't work, suspect a brush bar motor. It is a known fault on the DC24. There is an article here on the subject:

http://dysonmedic.co.uk/dyson-dc24-brush-bar-motor/

Angus Black
October 2011