What power supply did you use? To which pins / connector did you connect it.
What kind of short? From what to what?
The regulator is only in use when you connect e.g. a 12V supply to the barrel connector or the Vin (and GND) pins. As the board still works when connected to the computer, it is likely that the regulator is died; you can measure the 5V and 3.3V output with a multi-meter when connecting your external power supply.