I have a 2002 Protege I bought used with no manuals. The remote for the door locks has been deactivated. How do I reactivate the remote?

try this:
To program the remote is just short of doing the hokey-pokey. Note if you have more than 1 remote you must program the other remote at the same time. Are you ready? 1. Remove the key from the ignition switch. 2. Open the driver's door, does the warning system turn off? If yes, go to the next step. 3. With the key in the switch turn the ignition on then off and remove the key from the switch. Do this 3 times. 4. Close and open the driver's side door 3 times. If you've done things right you'll hear the computer buzz one time. At this point press any button on the remote 2 times. If you hear the computer buzz again you're still on the right dance step. At this time if you have another remote press any button on it 2 times and then you'll hear the computer buzz 1 time. repeat for a third remote. Once done wait 15 seconds and you'll hear the computer buzz 4 times. Your remote and Mazda are now dance partners. If you didn't hear the buzz you missed a dance step or there is a system problem. Note; this dance step is not compatible with over vehicles.