In Ubuntu 14.04 LTS, sometimes I click one of the icons on the left edge of my screen: the one labeled Software Updater. In some cases, after a successful update, I then click the Shut Down... menu item and choose Restart. While rebooting, the list appears in which I can choose my operating system; as always, I choose the regular Ubuntu. But after I do, the screen goes black and stays that way permanently, so I must physically power off the computer.

However, on all subsequent startups, everything works fine.

Is this a symptom of a problem I should worry about?

Thanks for any insight.