Either the valve body is blocked or the transmission is low on fluid. The valve body is located in the same side as the linkage, behind the cover. The passages inside can become blocked with bits of friction clutch material and if the flow is restricted, you'll get no movement from the trans itself.
Make sure the car has warmed up before checking the fluid. When the car is shut off, fluid can run out of the coverter and back into the trans and cause a false full reading. Always check it with the engine running, trans in neutral and the engine at, or near, normal operating temperature.