If your vehicle is showing car won't move at all when put in gear, here are the most likely causes and the parts you'll need to fix each one.
Automatic transmissions rely on hydraulic fluid pressure to engage gears and transfer power. If the fluid is extremely low due to a massive leak or improper filling, the transmission will act like it is in neutral.
If a CV axle snaps, the vehicle's differential will route all engine power to the broken side, resulting in zero power reaching the wheels. This can also happen if an axle pops out of the transmission after recent suspension work.
The clutch friction disc has worn down to the rivets and can no longer grip the flywheel. The engine will rev freely in gear because it is completely disconnected from the drivetrain.
The shifter inside the cabin has mechanically disconnected from the transmission due to a broken cable or shattered bushing. You are moving the handle, but the transmission is physically still in Park or Neutral.
A major internal component has failed, such as a shattered transmission fluid pump, a stripped input shaft, or a destroyed torque converter. The transmission must be removed and rebuilt or replaced.