There's a telltale LED on the remote located behind the red lens. Press and hold the button and make sure the LED illuminates. That confirms that the remote is working.

I assume the remote is original to the car? If just replaced it by purchasing one from eBay (like I did more than once), your money is gone - the remotes are paired with the car, and can only come from the dealer. They use the VIN of the car to know which "frequency" of remote is the correct one.

If the remote is original, and you see the telltale LED - verify your synching method - this is what you should have done: Aim transmitter at receiver, briefly press button. Within 30 seconds, lock or unlock the car with a master key (can be the key on the remote). It seems like I've also seen where you might need to lock and unlock repeatedly...

If you've tried this on the driver's door with no positive results, try it on the passenger door - the synch process works there, too.

If still no positive results, it's possible the keyless entry module in the trunk is kaput. This is the device that's paired to the remote, so be sure to get this from the dealer, after making a substantial withdrawal from your bank...