Your 2003 trailblazer start. The radio turns on and lights turn on.?

There could be a few reasons why your 2003 Trailblazer starts, the radio turns on, and the lights turn on, but the engine doesn't turn over. Here are a few possibilities:

- Battery: Check the battery to make sure it has enough power. If the battery is weak or dead, it won't be able to provide enough power to start the engine.

- Starter: The starter is responsible for turning over the engine. If the starter is faulty, it won't be able to engage the flywheel and start the engine.

- Ignition switch: The ignition switch is responsible for sending power to the starter. If the ignition switch is faulty, it won't be able to send power to the starter and start the engine.

- Fuel pump: The fuel pump is responsible for delivering fuel to the engine. If the fuel pump is faulty, it won't be able to deliver fuel to the engine and it won't start.

- Security system: The security system on your Trailblazer could be preventing it from starting. Try disabling the security system and see if it starts.

If you're not sure what the problem is, it's best to take your Trailblazer to a qualified mechanic for diagnosis and repair.