Diagnosis
The display showing "---" usually means the control board is in a factory default state or has lost its configuration. This can happen after a power cut or a glitch.
How to Fix It
The first thing to try is a full power reset. Turn off the dishwasher at its circuit breaker or by unplugging it if you can access the plug. Leave it off for a full 5 minutes. This lets the capacitors on the main board discharge completely. Turn the power back on. The display should briefly show something else, then settle. You'll likely need to reprogram your settings like the clock and any delayed start.
If That Didn't Work
If the "---" persists, the control board itself might be faulty and need replacing. Before you go that far, check that the door is latching firmly. If the door switch isn't engaged, the control won't initialise properly.
Heads Up
Don't just turn it off at the machine's button—that's a soft power-off. You need to kill the mains power completely for the reset to take.