when Gnome shell is used for some time, about an hour or more, i t hangs,
the mouse does not hangs.
So its the problem with gnome-shell.
Bug reported on redhat bugzill is availiable at bugzilla.redhat.com.
So for those guys this is really an annoying thing, there is a temporary solution .
Go to tty1 by pressing
Ctrl + Alt + F1
Now login using user name and password, (Number pad doesn't work here)
On successful login
Now go back to GUi by
Ctrl + Alt + F7