Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Is anything else acting up? Fuel gauge, radio, airbag light (when the key is first turned to on)?
Do you have a scan tool to check for communication with the PCM?
Do you have a spare key that you could try?
It sounds like either a PCM issue or a short somewhere.
Have you checked the starter relay and the 30 amp starter fuse?
Any voltage reading at the starter?
One thing you might try:
Unplug the coolant temp sensor from the side of the radiator.
If this sensor is shorted internally and telling the PCM that the car is overheating it would cause the fan to run constantly and could prevent the starter from engaging.
If your car has the 1.6l engine the sensor is in the back of the engine block.