Try the following:
1 - delete the iPhoto preference file, com.apple.iPhoto.plist, that resides in your
User/Home/Library/ Preferences folder.
2 - delete iPhoto's cache file, Cache.db, that is located in your
User/Home/Library/Caches/com.apple.iPhoto folder (Snow Leopard and Earlier).
or with Lion, Mt. Lion or Mavericks delete the contents the User/Library/Containers/com.apple.iPhoto/
3 - reboot, launch iPhoto, reset its preferences and try again.
NOTE: In Lion and Mountain Lion the Home/Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and press the Return key - 10.7: Un-hide the User Library folder.
If you're running Mavericks, 10.9, go to your Home folder and use the View ➙ Show View Options menu to bring the this window:
where you can check the Show Library Folder checkbox.
They have to be on your laptop. If you've used iPhoto there will be a preference file and cache files. Did you make your Home/Library visible as shown in the screenshot?
Download and use Find Any File to search for: 1 = "com.apple.iPhoto.plist" and the folder "com.apple.iPhoto".
I've located the file - thanks, and deleted it. I've resterted my laptop and launched iPhoto but I still have the same problem! Just worth a mention (this is not a result of your proposed fix) when I select all the photo's in a specific album and then click "Slideshow", the photo's are played in reverse order? This is all very strange! Thanks for your helpso far.