Power Door Locks Don't Work

I have a 99 Dodge Ram and I can hear the electronics and mechanisim attempting to lock or unlock the doors but they don't move up or down.

This has happened on both doors, however if I sit there long enough and play with the switch (push it up then down, up then down, up then down) eventually it will lock or unlock. Anyone know what could be causing this?

Thanks

Magnum

This happened to the wife's truck, I had to take off the door panels and replace the linkage to the lock.