I am using Linux Mint 17 Cinnamon. When I lock the screen it shows a dimmed version of my desktop background and the time. So when I want to unlock it, I usually move the mouse and the prompt for entering the password appears. However, sometimes it appears rather slowly and today it didn't appear at all. I saw my mouse moving, but no matter how much I moved the mouse, clicked and typed the password prompt wouldn't appear. I thought this might have to do with the fact that I use an external screen with my laptop lid closed, but after I opened the lid nothing changed and I was still not able to unlock it. Finally, I restarted. So my questions: is this is a known issue with Mint and is there a particular way to call the password prompt?