Just yesterday I updated my Ubuntu; from 12.10 to 13.04. Everything was working fine in 12.10. The first time after the update when I rebooted, 13.04 worked seamlessly. But later every time, I log in, the login & guest dialogs remains on the screen. The panel doesn't work properly. The applications hang a lot. I use a Lenovo E430 laptop. I've gone through all the other topics regarding the same. But haven't found a solution yet.