What MacBook model specifically? What have you done before you shut it down? Do you still have the Restore DVDs (the gray ones) or a SL Upgrade DVD to run Disk Utility from it?
I don't recall excatly what I did.... Just normal use. No system type installs/changes/etc. Normal meaning playing music and writing a document in Word. Then when done, just "Shut Down."
Yes, I have the Install DVDs. Was thinking about installing OS again.
However, I just realized that the easiest thing to do is to take it to a genius at the Apple Store.