After you've backed up everything, I suggest you delete the iPhoto preferences and cache (iPhoto should not be running when you do this.) When you restart iPhoto, new (clean) versions of these files will be created. Note that any change you have made to the preferences in iPhoto will have reverted back to its original setting.
I recommend making a copy of these file first—drag them to the desktop. (Keeping a copy will allow you to quickly revert to your earlier settings.) Then delete the originals.
They are located in the Library folder of your home directory. This folder is hidden by default in Mountain Lion (I presume that's the OS you're running? That's what your profile says.). To see the hidden folder, open Finder and click on the "Go" menu while holding down the Option key. "Library" should appear on the drop-down list. Select it, and the Library folder will open.
Here are the files to delete:
~/Library/Caches/com.apple.iPhoto
~/Library/Preferences/com.apple.iPhoto.plist.lockfile
~/Library/Preferences/com.apple.iPhoto.LSSharedFileList.plist.lockfile
~/Library/Preferences/com.apple.iPhoto.LSSharedFileList.plist
~/Library/Preferences/com.apple.iPhoto.plist