If you've checked that the outlet that the CT is plugged into works, there are a few things I can suggest checking if you're so inclined - otherwise, send the top to Festool for service.
1. Does the Manual/Offf/Auto switch feel sloppy at all, or are the the positions quite positive?
2. When in the Manual setting with the CT plugged in, does adjusting the suction/speed have any effect?
3. Any damage to the power cord?
4. Check the brushes. If worn out, a pin will spring through the face of it, preventing the machine from running. You can order replacement brushes if required.