I appear to be having a similar yet different issue. My windows 7 PC shows that Arduino Uno is connected to the PC and it says there are no issues. However when I try to update the firmware it says that nothing is connected and no com port found. I am using my Uno on an x-carve and I have recently added a laser and tried to flash and update the firmware with continue errors and issues all the time. I went back to my mac laptop and it can find it, but it does not seem to be communicating correctly as it can no longer move my router. Ive spent 3 evenings on this trying to fix it and I am at a loss.