My Macbook Pro 2014 ran out of battery while mid-slideshow. Now the slideshow won't skip through photos and I can't figure out why? Macbook Pro 2014 13-inch Intel i5 8GB RAM 128GB flash, iPhoto library is on external HDD

Question

Macbook Pro 2014
13-inch
Intel i5
8GB RAM
128GB flash SSD,
Integrated Graphics
iPhoto library is on external HDD
I was in a slideshow, with around 1,911 photos in it. About halfway through, my Macbook ran out of battery. Now when I restarted and charged the Macbook and reopened iPhoto, the slideshow won't advance through photos, and I can't figure out any reason why it would do this.
I thought it may be corrupted, so I deleted and reinstalled iPhoto library, iPhoto itself, and disconnected and reconnected my external HDD.
This didn't work, the photos still won't advance.
I don't know any reason why this would be happening, and there is ample space on my internal drive.
I'm happy to provide more information if needed!
Many Thanks,
James

Answer 1

Make a few tests, James, to narrow down the problem and find out, if the slideshow is corrupted, your iPhoto Library, or settings in your account.
To test, if only your slideshow has a problem, create a new slideshow, just for testing. Just use "File > New Slideshow" and add a few photos. Does this slideshow play correctly?
If the test slideshow does not play either, create a new iPhoto Library. Use the File menu in iPhoto: File > Switch to library > Create New. Import a few photos and create a slideshow.  Does it play?
If even a new library does not solve the problem, test in a different user account (see this document:  Isolating an issue by using another user account - Apple Support):   
This process involves creating a new user account, logging in to it, and testing for the issue.
Create a new standard or admin user account in Users & Groups preferences.
Use these instructions for OS X Mavericks.
See these instructions for OS X Mountain Lion.
See this video, or these instructions for OS X Lion.
Optional: If you have any specific files you wish to test with, copy (don't move) those items to the /Users/Shared folder in the Finder.
Log out of your current user account by choosing Log Out from the Apple () menu.
Log in with the new account you created.
Attempt to reproduce the issue you were seeing in your regular user account.
After you have completed testing, log out of the test account by choosing Log Out from the Apple () menu.
Log in as your regular account.
After you have completed all testing with the test user account, you may want to delete it. You can delete an account in the Users & Groups pane of System Preferences.
Note: Prior to deleting a test account, make sure you are completely done with it. If you have files in the Guest User you wish to keep, you should copy them to the /Users/Shared folder .
If you should find, that slideshows only play in a new user account, post back.