Hold down Option when when you start iPhoto. It should ask what Library to use. Hit the “Create New” button. If it starts your library is corrupt.
If that doesn’t work you should try deleting the plist file that iPhoto uses. The easiest way to do this is open the Teminal.app in Applications/Utilities and enter:
open ~/Library/Preferences
and hit enter.
Then find com.apple.iPhoto.plist and move it to your desktop. Then try opening iPhoto and see if it works.
If none of that works you can at least get to your photos by going to your Pictures folder and find iPhoto Library. Right click or command click on it and select “Show Package Contents”. Originals of your photos are in the folder called Masters.