As Nikon has several different AV format, what is the exact CODEC in the MOV files from your camera? That will probably determine the issue. My guess is that the CODEC is H.264, but we need to be sure.
Also, since the format is MOV (can have all sorts of "stuff" inside that wrapper), what version of Apple's QuickTime Player do you have installed? QT Player, with the correct CODEC will be necessary.
Good luck, and please let us know a bit more,
Report back with the codec details of your file, use the programs below... a screen shot works well to SHOW people what you are doing