Thevenin Voltage with only Dependant Sources?
If a circuit doesn't have any inputs, Vth will be zero.

If you do the equivalent, you can only get the resistance as seen by one of the terminals using an external source and use Ohm's Law to find Rth viewed by that "new" source.

So, if there aren't any inputs, you get an equivalent circuit with Vth=0 and Rth=Req.