Actually, my cable solution only worked for a short period, then it stopped again. So I tried the pigtails to the screen, as per Rod H's post. But again, it still only worked for a week or so. Then I had a think about the connections to the screen: they come into the same small sub-board as the USB connection, and both the USB power/signals and the touch screen signals go through another pig tail connector to the main board. I thought that it is possible that the movement of the plugging and unplugging of the USB (as per Andre's original post) might disturb the connectors. So I reseated the pigtail connector going to the main board as well. That was over a month ago, and the problem has not come back. I hope this works for you as well.