Since it's stuck on the lock screen you might have to make or use recovery media to restore it to factory condition. I hope this is not one of those users that doesn't backup their stuff.
I have a I have a Dell Inspiron 15 3000 which does not have any password, only I click log in on the menu and it goes to the main screen. I had to shut down the laptop speedily without closing the back ground apps and now when I turn it on, it is only going to the screen with the time and date and when I click or press anything, the icons on that screen is flying up and the lock screen wallpaper is showing. The actual screen with icons and the screen is not showing and nothing is working. Please help D;