Shift lever will move, but the gears wont shift. Is it the lever or the gears? on 2006 Buick Rendezvous

Came home last night and parked in the drive way, car ran fine and shifted fine. Next Morning dad tells me gears wont shift but the lever still works. I'm thinking the lever might be worn down and isnt cicking anymore. How can i tell if its the gear shift lever or the gears themselevs.

Asked by for the 2006 Buick Rendezvous
Check the cable on the transmission linkage, might have come loose.