When did 3 astronauts die in a shuttle before it took off?

No fatalities have ever occurred on a shuttle prior to launch.

3 astronauts did die on January 27, 1967 during a test for the Apollo/Saturn-204 launch, also known as AS-204. Command Pilot Virgil "Gus" Grissom, Senior Pilot Edward H. White, and Pilot Roger B. Chaffee died when fire broke out inside the capsule.

AS-204 was later officially renamed Apollo 1.