my computer is running 12.04. It takes a loooong time to restart and im keep getting notifications that Ubuntu couldn't download from the repositories. I want to reinstall the whole system but there are a lot of programs with setups that took a long time. Is there another option for me? Possibly to upgrade in some special way so that it fixes the problems I'm experiencing?

also, once i upgrade (or totally reinstall the system), what is the best way to speed up the boot time to as short as possible?