Shot a wedding tonight.. just got home. Had a few moments of panic while I was shooting the first dances. I was shooting them a little differently than I normally would, with just one on camera flash. The D750 being new to me, I don't know it as well as I'd like. One second I was shooting the first dances getting good results, the next second the flash absolutely will not fire. Doesn't matter what I do, even the test button won't fire it. My trouble shooting went like this: 1.) Flash is on and seated in the shoe. Batteries are fresh. Turn flash and camera off and back on. Remove flash and re-inset in hot shoe. Still no flash. 2.) Begrudgingly shoot the parent dances with ambient only using the DJ's colored lights for fill, with the knowledge that I'll have no choice but to deliver these shots in black and white to hide the color casts. 3.) Said screw it after the parent dances, went and got my D500 and threw the flash on it. Worked perfectly. Swapped the 24-70 onto the D500 and went back to shooting. Shot the rest of the night with this combination because I didn't have time to troubleshoot the problem. Just got home and took a minute to look at it. Realized that if you hold the flash button and rotate the rear command dial you can disable flash. This somehow got bumped, and I didn't realize that this option existed so I wasn't able to quickly diagnose it in the heat of the moment. Lessons to be learned: - Don't use a camera for a critical event 4 days after you take delivery, it's a recipe for disaster. But I really wanted to test it out in a challenging environment. -Know your camera like the back of your hand. Then study it some more. -ALWAYS have a backup for every piece of gear. Even if you don't break something, you may not have time to trouble shoot a simple problem in the heat of the moment. Luckily I was prepared and this only cost me color in a few shots. But if I didn't have more flash units and a second body, it could have easily ruined my photos for the rest of the wedding. This is exactly why you shouldn't start shooting events professionally until you have enough gear and in depth knowledge of how it works.