I had a similar problem with my C40TT.

The steering wheel connects with a chain sprocket at the bottom of the compartment on the back. There is a switching mechanism below the sprocket which changes the drive motor from the front wheel motor(s) to the small motor on the steering wheel. This is a combination dual dual switch. There are two buttons on one side that control left turning and two on the other side that control right turning. There is an engagement switch that engages the small motor and a cutoff switch that disengages the main drive motors for extreme turning so you don't tear off/drag the steering wheel. On my unit one of the switches that is a cutoff switch was stuck down and would not release thus killing the power to the main drive motors. I pulled it out with needle nose pliers and worked it back and forth several times to loosen it up and it works great.