I have a craftsman dyt 4000 lawn mower. I was mowing and the blades quit turning. So I turned the motor off to check the belts and now it won't start, not even a click when key is turned on.

Sounds like a belt broke or a safety switch has locked out the ignition. Try to give us more to go on and check that model number, never heard of dyt 4000. Model number is usually under the flip up seat on Sears.