Sounds like you've started up into Single User Mode. Single User Mode can be activated by holding down command(apple key)+s. I'm assuming that is what happened.
Once it gets to the root# prompt, you should be able to type
exit, causing it to show a few more lines of code, and then boot into the normal graphical interface. You can also type
reboot to restart the machine from the root# prompt, which might also fix your problem.
That's as far as my expertise goes. If that doesn't work, check out
this article about how to find out if your disk is damaged or not.
Cheers