Q: get ! message when double click on a photo in iPhoto

The exclamation point will be shown,when iPhoto has lost the connection between the thumbnails and the original image files. Then it cannot display the full image.

Try, if rebuilding the iPhoto library will help,  see this document:  http://support.apple.com/kb/HT2638

If iPhoto's rebuild does not help, try rebuilding with iPhoto Library Manager, see Old Tod's post here:   Rebuild the iPhoto Library

But before rebuilding,  backup your iPhoto library, just in case.