The post that the screw goes into in the cold water shower knob continues to turn both ways and no water comes out of the faucet.

Is your handle completely engaged ? Looks like it is slipping...
What kind/type/brand of faucet is it ? If not sure, post photo. We'll ID it ourselves...

Please respond to Milo.

It probably be very simple as to replace the knob, Thanks.

John

the post that the screw goes into in the cold water shower knob continues to turn both ways and no water comes out of the faucet.

Here's the diagram you wanted. If the handle slips on the shaft they have "fits all" replacement handles, (see image) Good luck, Tom