I've been caught by this a few times - do you happen to have a Custom Bank setting that uses AF-ON to activate Autofocus? Three out of the four banks I have use that, and I get caught all the time because I'm half-pressing the shutter button like an idiot and nothing happens.
Hmmm... Not sure I understand, all 4 banks are set with AF activation on. Nothing was changed since my last shoot, and yet it suddenly won't focus. I keep thinking something on the exterior of the camera must have been touched but I can't find what...any ideas?
You may also consider going to NikonUSA.com and getting the phone number for technical support. They are there all day and most of the night and have been very helpful to me in the past. I believe that if uoi just do a reset of all your settings to the factory defaults, you will lose all of your special settings unless you record them to a flash card first.
HAH! I'm almost embarrassed to tell you - but what the heck ..... I had grabbed my camera out of my Think Tank bag which is super snug after shoving it in there quickly after a shoot and apparently when I grabbed it on the run yesterday, it rubbed the Focus Mode Selector and slid it to M. I know I know - should have been the first thing I checked, and I thought I had, as its the first thing I thought of ... but I must have missed it or been interrupted or whatever and went immediately into OMG WHAT IS WRONG - MUST TALK TO MY NIKON BUDDIES mode. This a.m. with a clearer head and the decision that I would have to use Camera #2 while this one got fixed I calmly went over everything again .... and then kicked myself. So thank you all for your kind help .... just sign me "idiot"