Port 3 on our cortex doesn’t work and I can’t figure out whats wrong or how to fix it. Any ideas?
have you checked that it’s not just motor controller issues? If yes but they aren’t the problem, then get a new cortex
You stole what I was going to say 
Also try a new motor.
well, what can I say?
Obviously, check that your code is fully functional and is actually telling the Port3 to do something. Failing that create a blank document with your #pragma statements and run the RobotC debugger (assuming you use RobotC) and the motor debug panel so you can manually manipulate the speed being sent to the motors.