One of the signature troubles facing iPhoto users is the infamous gigantic exclamation point. This symbol, a grotesque and pixelated alert, informs you that the photo you were hoping to expand is no longer associated with the thumbnail that you clicked. Forums on this topic go into some of the problems associated with this issue.
Good news though! iPhoto comes with some troubleshooting solutions built in. To access some of these solutions, with iPhoto closed, press and hold (Option + Command) and click to open iPhoto from your Dock. The following window will appear:
At this point, select the options you wish to complete before iPhoto opens. Some actions take longer than others (noted in the dialogue window). For the gigantic exclamation mark issue, try running the three checked boxes in the example above.
Is your iPhoto Library getting too big? The more photos you have in your library, the longer it will take iPhoto to open. To remedy this, users can make a new iPhoto Library file. To start a new iPhoto Library, with iPhoto closed, press and hold the Option key and click to open iPhoto:
Choose the destination for your new library and you are all set. You can even put the new iPhoto Library on an external hard drive. Now, iPhoto will default to opening the newly created library. To access your old library (and change the default library iPhoto will open), simply press and hold Option and click to open iPhoto. Select "Other Library" and choose which iPhoto Library to open (the default location is username > Pictures). Users may also be interested in checking out Fat Cat Software's excellent iPhoto Library Manager, should they be looking for a more robust solution to multiple iPhoto Libraries.