Computer does not recognized Leonardo USB

Hello Everyone,

I have a recurring problem with the Arduino Leonardo. Currently, it has occurred on three boards. For all three, I was able to program the microcontroller for a few days, but eventually the computer stopped recognizing them. When I plug one in, the computer registers the Leonardo for a few seconds, and I am able to select the com port which it is located. However, after 10s or so, the menu item goes gray, and the board is no longer recognized. I have tried the leonardos on four computers, three of which run windows 8, and one linux machine. On each I have tried to re-install the arduino ide and drivers. Doing such has made no difference, even when different cables were used. I appreciate any advice which can be offered.

--Timothy

I have the same problem here. The PC recognized the Leonardo on COM6 once. I ran Blink for testing. After that I wnated to upload my sketch, but since then my Win7 PC has not recognized the Leonardo anymore. I did restart the application, my PC changed USB ports, reset the Leonardo etc. but to no avail. Has anybody solved this mystery so far. It cannot be a user issue, because I have read abot this problem many times and there never was one distinctive solution.