The crack was in the solid rocket booster and once lit, it cannot be shut off. The liquid fuel engine, all launch vehivles have them, can be shut off by turning off the fuel pump thus starving it of fuel.
All of today's rockets are bolted to the launch floor. Even with full thrust the rocket cannot take off until the bolt are cut. These are called pyrobolts because they have explosive which is used to sever the bolts.