Madrat is correct though. If that pointy piece of plastic that meets with the black lever by the clutch knob underneath the vacuum is snapped off, you could try gluing it back on. If not, you'll need a new chassis for your Dyson because it's part of the main body
It's not actually that hard of a job to replace the chassis anyway. Most of the parts pop off without any screws. Just 3 screws for the clutch cover, 2 screws for the switch housing and 4 screws for the motor unit!