If a window crank just spins when it is turned, that typically indicates a stripped gear in the crank mechanism. Cranking mechanisms that are stripped need to be taken out and replaced to correct the problem. A stripped gear can mean just a broken handle or a damaged operator mechanism. You can repair a handle crank mechanism in your home by first making sure you have the correct replacement part.
Examine the window crank to see where the gear has been stripped. The threads on the handle may have gone bad, or the splines on the operator mechanism may be bad.
Open the window, using a pair of pliers to turn the crank while pushing out on the window.
Press down on the guide arm to remove the bushing from the track. The bushing is a small roller that moves up and down the track that opens and closes the window.
With the screwdriver, remove the trim screws that secure the casement cover.
Remove the screws that secure the crank mounting. You can then pull out the crank or operator mechanism.
Set the new operator mechanism in place and align it with the screw holes on the casement.
Insert the screws into the screw holes and tighten them with the screwdriver.
Replace the casement cover and secure it using the old trim screws and the screwdriver.
Pull the window inward and put the bushing back in the track.
Screw on the handle that came with the new operator mechanism.
Replace the crank handle with a new one if the threads are damaged on the handle. A power drill can be used instead of the screwdriver to remove the screws from the casement cover and the crank operator.
If screws were not used to secure the trim cover, pry off the trim cover but be careful not to break it.