chain saw ?

Assuming the engine is running. Have you made sure the chainbrake is off? The brake stops the chain moving, and if you try to operate the throttle the engine revs will not increase.

If the chainbrake is off and the engine revs pick up but the chain doesn't move the sprocket might be worn down, or the clutch needs replacing.

If the brake is off and the revs don't increase it's probably a carb fault.

Any other symptoms?

wes
May 2009