ipod appears in finder but won't show up in itunes

my ipod shows up in the finder but won't show up in itunes. something is going on though, because when i plug in my ipod it will launch itunes, and at one point itunes was "calculating disk space" after i plugged in the ipod. so it's almost as though itunes itself is having an issue displaying it--but i just ran an update.
this happened a few weeks ago, however it did show up in itunes on one of the 3 macs (mine) that i tried. now it won't show up on mine either.