I'm not a wireless flash guru, I've only played around with it a little bit, but I strongly suspect that it's a setting in the SB-800 and not the camera that's causing it not to fire. I'll just speculate that if the SB-800 is set up to act as a wireless remote unit, it may disable it's ability to fire when mounted on the hot shoe. You may get a faster answer regarding this over in the "flash and lighting" section of Nikonians - there are some really talented, knowledgeable flash gurus over there.
Larry, If you don't know what setting to change, reset the SB-800 to the factory default settings by pressing the MODE+ON/OFF buttons for approx. two (2) seconds. This will clear any setting you might have changed causing your issue.
Hope this helps...JL
________________________________________ 45+ years of Nikon ownership and counting Visit my SmugMug gallery
Another thing that could be at work is that you may not have the flash properly seated in the shoe. I had that once, and thought I must have been a nitwit, but closer inspection showed that the shoe was actually slightly bent on one side and was not allowing the flash to fully seat. I unbent the shoe rail and it works fine now. Oddly enough I had the same thing happen on a different camera a couple of years later. I don't think it's an entirely rare circumstance, although my cameras do travel a lot more than most.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!
Thanks everyone. Like others here, my camera travel quite a bit and it would seem the issue was with the angle of the shoe. I tried all the suggestions listed here and now, everything is working just fine.