Just connecting 5V to ground shouldn’t do damage, the voltage regulators are current limited (although the USB port is probably not.) As to what to do I’d try removing all the wires except the power (wall wart or USB) to the Arduino power led comes on and see if the Arduino is recognized by the IDE. Try powering it from a wall wart if you are on USB. Try another USB port if you are powered by USB (that would indicate that the original USB port may be blown.) If none of that helps then you have likely blown the Arduino (and possibly the USB port too) and need to replace it.
Peter