I had the LG 4K display for a day and it worked great with the new MacBook Pro and Windows machines (!), with gorgeous colors. But the next day I go to plug a computer into it and the speakers work just fine, but the display remains dark. It won't light up when connected to the MBP or Windows machines it was being used with before, and there doesn't seem to be any controls to reset any configuration of any sort in the monitor. I got my genius bar appointment, but is there anything else I can try until then?