I've installed FLIP, and I can see how it should normally work, however since the board isn't communicating with the computer at all, I don't think I can do much from here. The guide you linked presupposes that the computer at least recognizes it as an unknown device or that you're trying to wipe the existing firmware after having been able to use the board successfully in the past. For clarity I'm on the Uno R3. Should I consider just buying a new board, or am I missing something entirely? Thanks