I'm having this problem now, too.
I updated the Zune software to 3.0, and now it doesn't recognize the Zune (making me unable to upload music / update the firmware)-
but Window's sees it everytime I plug in my zune and tries to 'install new hardware'- but then tells me that I have to contact the manufacturer for drivers.. I click "check for updates" & it tells me that I haven't plugged the zune in yet. Any suggestions? Haha.
edit: I should mention that I tried installing the 2.1 software as was mentioned earlier in this thread, but it did not work.
Also tried system restoring but it kept coming up with errors..