The excclamation point is caused by your having done something, anything, to your photos in the library in finder. Users are not meant to do anything to their photos in finder, do whatever you want to do to them from within the app itself. Stay out of the finder!
You might also try rebuilding the library following these instructions:
http://docs.info.apple.com/article.html?artnum=107947 If the first, easiest option does not work, read further down and try the manual rebuild. You may well end up with duplicates (as it says), but it will be worth dealing with them in order to salvage your photos.