Just got a 1974 Super Beetle 4-speed that had been stored for the last 5 years in a shed. It had never been run during that time, and, predictably, it won't start. Battery has been replaced. When the key is turned (car in neutral or in gear w/the clutch pedal depressed), you can hear the starter engage to try to turn the engine over, but nothing happens -- zero rotation.

Additional likely relevant info: In neutral the car can be pushed. If the transmission is in gear with the clutch pedal depressed, the car cannot be pushed.

Any thoughts on where to start the unfreezing process?