Look at a Valterra cable operated valve at an RV parts supply,
or on the internet (Amazon carries them).
Helps to see how it operates - and the cable connection.
"Old Biscuit" posted some pics of the various valves on this thread -
Scroll down on Page 2 The cable *may* have pulled out of the connection at the valve.
Or - the cable may have kinked inside the sheath.
(The cables are really almost impossible to break)
Suggest buying a replacement cable and sheath.....
However, just buy a complete assembly in case your valve is broken.
Not that expensive - and you have everything you need.
BTW - try the cable replacement *first* rather than replacing the
entire valve - 'cause (I can vouch for) replacing the valve is a "PITA"...:(
.