This happened to me this morning. There was an 'up' arrow under the hard drive icon -- which I clicked and then was taken to what appears to be my normal operating desktop. Except there were other problems. When I attempted to type in Safari (google search, passwords, etc), my writing was always in alternate characters. Checked preferences for Safari, and they were as they should be (english). Shut down and rebooted. Still got the hard drive icon, and still have the jiberish text when typing.
Any more info out there about what the hard drive in the center of the screen is supposed to mean? Is my Mac running in some sort of 'safe' mode?