How do I diagnose drive shaft problems on Megane?

After loud crunch and loss of drive on my 02 Megane diesel - got car home and RAC guy suggested drive shaft problems. Now have car jacked up. Engine runs fine, gear selection and clutch operate fine. Both front wheels rotate freely along with driveshafts (but with clicking sound) when gears engaged - driveshafts seem ok - do these symptoms only leave gearbox diff as the failed part?