wow, i cant believe that none of those worked. I guess the pins could very likely be bent (on the phone) then. device manager should have recognized at least an unknown device...
only other thing i can think of is to try a usb port on the back or something else in the front. you need to confirm that all USB devices are ok...
also may want to check the services and make sure all appropriate ones are running.
see here:
http://docs.info.apple.com/article.html?artnum=305716
if all else fails, reboot?
hopefully we can figure out what exactly is going on...good luck!