Dell does it again... The recent BIOS updates across several models (9550, 5510, 9360) seem to cause intermittent connection/disconnections of USB devices connected to docks, the way some of us recall from about a year ago. Some were unable to roll back to the previous stable state or even managed to wreck their Windows installations. If you have been hit, please yell at Dell support vigorously ASAP, to pull the updates and fix. Otherwise, hold on with the update until a couple of weeks after reported safe.