Grey screen, image of mac HD? WHat happened??

[WilliamBos]

Last night when I turned on my mac for my nightly computer time, it booted up to a grey screen with an image of my mac HDD, and a drop down with three options. One was showing my IP providers name, and the other had three *** and the third was an X with a check mark to the left of it. I tried them all, and the one with the x worked, it went to the normal log on screen options.

Then I started to repair permissions, but was late and needed sleep. Fearing leaving to complete, I stopped and shut down. Today, it started up normal.

What was the cause of that?

Going to pick up an external HDD, and run time machine. Won't be able to get out until Monday though...