I recently installed Ubuntu 13.04 on my Lenovo G580. So everything went alright, then I installed Kubuntu to try it out, and it was pretty laggy then I uninstalled it so everything got messed up and I got confused, So I just decided to format Ubuntu and install it again. After I installed it and rebooted, I got an error message saying: "Ubuntu is blocked by the current security policy.". Can I get some helps?
I believe that you are installing Ubuntu over an existing installation, without cleaning up/re-partitioning your HDD/SSD.
Formating Partitions using LiveCD
You can do the following in Ubuntu's LiveCD after installing gparted, but I prefer to use Parted Magic. At the time of writting, you must burn this image to a CD/DVD or use the lateset UNetbootin, which is not available in the repositories.
Installing gparted on Ubuntu LiveCD
Formatting your partitions