In that case it sounds like the wheel that does not turn is loose on the arbor. This will stop the power transmission to the rest of the gear train and will allow the barrel to just turn. If I remember rightly on these french clocks the pinion gear(the silver one) is cut on the arbor(the axle) and then part of it is turned down and the wheel is riveted on to it. To repair this properly you would use a brass split stake in a vice which would allow the pinion gear to sit in a hole, the wheel would be facing up and would give you access to the part of the turned down pinion gear which just comes through the hole in the centre of the wheel. You would then use a punch with the outside diameter no bigger than the diameter on that part of the pinion and which also has a hole in the centre to allow the arbor to pass through, and just keep tapping at it until the wheel is again solid on the arbor. If you do not have the tools to do this your only other option is to try some of the strong loc-tite glue mentioned a couple of posts ago. Being that this wheel is so close to the barrel it will be taking a lot of power and I dont know if this would be a permanent fix i.e. how long a glue joint would last.