Diagnosis
You are in diagnostic mode. The three lights likely indicate a specific fault code. This mode activates from a specific button press sequence.
How to Fix It
Press and hold the Cycle Select and Start buttons together for 3 seconds. This exits diagnostic mode. The display should clear. Select your desired cycle and press Start normally.
If That Didn't Work
If it re-enters diagnostic mode on its own, you have an active fault. Note which lights are lit. Common ones: Heater, Sanitize, and Clean lights often indicate a heating element or temperature sensor failure. You will need a multimeter to test continuity.
Heads Up
Do not ignore persistent fault codes. A failed heating element can cause the dishwasher to not dry dishes or run extremely long cycles.