Remote start not working

Is this the factory remote start? Your are pressing lock then the start button twice in 3 seconds? Do the power locks work correctly? If you start it normally is the check engine light staying on? If yes to all three of the first items and the check engine light isn't on you will need to use a dealer level scan tool to check the body control modules operation when the remote is used. It uses a data signal through the remote entry module to tell the powertrain module to start the engine. That module also receives the signals for the tire pressure sensors. The scan tool can be used to tell if the module is sending the signal or not and if it is it will show if the signal to the PCM is being acted on or not.
The only other item that could cause an issue would be the hood switch which can stop the system from working, but it will normally stop the door lock operation as well.