The second generation Prius (model year 2004-2009) has a digital dashboard (officially called the “combination meter”, also known as an “instrument cluster”). It is prone to failure, resulting in no lights at all, in the center display or on the sides, with the exception of the “check engine” light which is controlled directly by the engine ECU (thanks to emissions regulations).

The car will still drive but it can be stubborn to shut off; usual presses of the “power” button may be disregarded (holding for 3 seconds (safety override) will work). The rear hatch can also refuse to open. Both of these symptoms stem from the car’s communication architecture; permission to turn off the car and open the hatch depends on vehicle speed, which the meter is responsible for reporting to other computers.

The circuit board, made by Yazaki, has a flawed design, even in later models. Eventually the components get out of tolerance and the board will power off. This will happen upon startup in cold temperatures. Toyota has issued a technical service bulletin describing as much (T-SB-0172-09 also embedded below).
But the condition may also occur when driving, out of the blue, in. Restarting the car may get the meter to come back.