If you also have a USB in your keyboard for a mouse, then this might help:
I saw a post in another forum here where one person removed the usb drive for their MX mouse and it fixed it. About an hour ago I also removed the usb drive that was in my keyboard, then tried a Restart, and happy to say it started fine and without a problem. Now, mind you, this was just one Restart but I am thinking that was my problem. I should note every time before on Restart I would get a popup saying they couldn't find my "keyboard," which is wired but had the mouse USB in it. And I guess that is what it was referring to, that it couldn't find my mouse.