How Bootload an Lilypad Arduino USB using Arduino UNO I recently bought two lilypads USB, one works perfectly (it's recognized in my computer, but the other one it's never recognized, I even try in different computers and the same scenario with both devices) 



So I think that maybe the second one doesn't have a bootloader installed. So I'm triying to "burn" a new bootloader. I have been triying following the guide on https://www.arduino.cc/en/Tutorial/ArduinoISP using as programmer an Arduino UNO but without luck. I ever get avrdude: Device signature = 0x000000 (retrying). Thanks for the help!
If you try uploading to a LilyPad USB with the wrong board selected, you may end up in a condition where the bootloader can no longer respond normally. 

You can get the LilyPad Arduino into bootloader mode by tapping the reset button twice in under a second. Once in bootloader mode, the LED should blink at about 1Hz for about 8 seconds. My advice is to load a blank sketch (i.e., nothing in loop() or setup()) and then double tap the reset button shortly after hitting the upload button. That should restore the LilyPad USB to a working state.