Following an hour in standby mode, my HP device has developed a very thin vertical white line down the full depth of the screen, about an inch in from one side, maybe one pixel wide. It is continuously visible as a steady line (most of the time), but sometimes flashing randomly regardless of the displayed image, including the desktop. During the brief moments when it is off, the background colours directly behind are unaffected. I've tried adjusting the screen resolution without success, but otherwise running short of ideas. It's not a major issue but more the irritation factor. Any suggestions for a cure?