Is it possible to fix a broken EV3 Port? I have an EV3 running RobotC version 4.55. 

The medium motor connected to Port A does not run, but if I connect it to another port (B,C,or D) it works. I tested it manually through the EV3 motor tab and with a program. I also tried connecting other motors to port A and they do not work there. 

Is there something I can do to "revive" port A?
It sounds like the polyfuse (the fuse that protects the motor circuit) or the motor driver (the chip that switches power on and off to the motors) has failed.

You can contact LEGO customer support and let them know about it. They will probably replace the EV3 if it is determined to be defective.

Or, if you are the do-it-yourself kind of person with surface mount device soldering skills, you could attempt to replace the components yourself.