I was using my laptop which runs Ubuntu 13.10 and wanted to switch workspaces. I'm not exactly sure which keys I pressed, but after pressing [ctrl + alt + arrow key] to switch workspaces my screen turned purple-black (I'm colourblind) and asked for my login and password. I have no idea what my login is, I've tried using the name of the laptop and then the appropriate password but after about two seconds the screen will display "Incorrect login". I'm not sure how to fix this issue, it happened on multiple occasions and at random, causing me to have to reboot my laptop. Again, the laptop randomly turns to a purple-black screen and asks for 'eric-laptop login' (name of the laptop), and a password.