Did a pretty thorough search of Google and this forum, and the solutions presented to my exact problem haven't helped, so here I am compelled to register!

Issue 1: Lightbox effects no longer load when photos are clicked, rather the photo loads directly in the browser window. Example from my site: http://www.guntonfilm.com/stills/on-set/

Images are hosted on NextGen Gallery Version 3.0.1. The plug-ins' built-in Lightbox effects are ineffective. Using Easy FancyBox Version 1.8.5 instead is ineffective. This is a recent issue, and I know plugin updates are usually to blame. To troubleshoot, I disabled all plug-ins except those two. Nope. Tried the "Save Header Area, Save Center Column, Save Footer" technique. Nada.

Then, after backing up all my custom Atahualpa options, I uninstalled and reinstalled the theme. The page linked above is what my site looks like with down-to-the-bone default settings. Lightbox still not working.

Switch theme to Twenty Fifteen... BOOM! Works perfectly.

Issue 2: Jetpack's Sharing Buttons. Now, this is currently not on my site because I disabled Jetpack like every other plug-in to troubleshoot the Lightbox thing. But when it was activated, I had social sharing buttons at the bottom of every page and post, hidden until you hovered over the "Share" button, at which point the Facebook, Twitter, etc buttons would emerge underneath. Except that, at the same time Lightbox effects stopped working, hovering on "Share" also stopped cold.

I'd appreciate any assistance, there's not a single theme I like more than this one. I need my endless customization!

Atahualpa Version 3.7.24
Wordpress Version 4.9.6
NextGen Gallery Version 3.0.1
Browsers tried: Chrome, Safari (cleared cache of both)

Sorry for the delay responding it was a holiday here and family was around all day. I’ll take a look tomorrow AM

So I have
Atahualpa Version 3.7.24
Wordpress Version 4.9.6
NextGen Gallery Version 3.0.1

With the NextGen default settings and it seems to be working fine for me - what are all the NextGen Gallery Setting and Other Options? (and there are a lot of them!)

Looking over the NextGen settings, it didn't look like I changed much from the defaults. Just to make sure, I reset all options. Nope, still opening images in the main window. I had another plug-in called Alpine Phototile for Tumblr that used FancyBox, and that also went the same way as my NextGen galleries (it's deactivated right now).

If you send me a PM with an admin ID/PW I'll take a look at the difference between our two sites.

What version of PHP are you running?

Php 5.5.22

I send you an email with a version of Atahualpa to try.

That did it! Slowly re-activating my plug-ins to make sure nothing breaks anything. Thank you!

Now if I can just figure out why the word "yes" is appearing at the top of every post and page...

Oops, that was a test I had in the theme. I was about to tell you what you had to do when I tried the login you gave me and that got me in and I edited the theme and removed the offending code so the 'yes' is now gone.

remember to remove that user.

I thought that might have been the case. Thanks so much for your help! Deleting user now.