How can I get my machine to work? - the motor runs but does not drive machi?

How can I get my machine to work? - the motor runs but does not drive machine, I retightend the stop motion knob, its still not working.
This is after I removed the outer stop motion knob with a small screw to clean etc but when replaced/reassembled it will not engage to sew/stich -
only the large fly wheel turns -
tried to get a service manual etc online or via youtube but no help....

Please let me know if I can download a free service manual from somewhere..
Hope you can help

Thanks