I own an Arduino Leonardo (not original). I got it yesterday and it worked flawlessly, today I plug it in and it isn't being recognized by Windows, no COM ports, no connection sound. What should I do?
Learn how to burn fresh firmware. You can do it with a $5 USBasp from eBay, with an Arduino UNO running the ArduinoISP sketch, or (if the existing firmware will go into DFU mode) with the Atmel FLIP program on Windows.