my iphoto stopped working, what should I do?

I was using the imovie, and then i closed my macbook, and then when i opend and tried to use the iphoto it didn't go. the message says " Shut down and restart your computer, and then open iPhoto again. If the problem persists, try rebuilding your photo library. To do this, quit iPhoto, and then reopen it while keeping the Option and Command keys pressed. You can also try restoring your photo library from a backup."

so I have shut it down, restarted, and did the reopen with the option and command keys pressed. i'm not sure how i can restore from a backup, but is there any other option?