Fedora 19 Gnome displays the cinnamon lock-screen and doesn't allow input, so you can not unlock.

Since one of the last updates, it happens, that sometimes the cinnamon-Lockscreen is active and it doesn't allow input.

To save your work , you ca kill the screensaver process cinnamon-screensaver 
 on one of the virtual terminals.

Use <Ctrl><Alt><F2>, login and terminate that process.
Change back to the GUI with <Ctrl><Alt><F1>

A detailed description can be found here