Try the following (in this order) to see if one will correct your problem:
(1) Restart Mac and then test mic again.
(2) Use your Mac's Disk Utility to repair permissions and then test mic again.
(3) Download and apply the latest Combo Update, for your Mac OS. At present,
the latest combo (10.8.3) is at http://support.apple.com/kb/DL1640
Repair permissions again immediately following the system restart
that completes the Combo update. Then test mic again.
(4) If your mic came with a software driver, install it again, repair permissions one more tim, and then test mic again.
had a very similar problem with a logitech C525, now working in mavericks ...
The audio port was shown in the system preferences as "unknown device". the first thing that helped was reconnecting the webcam but of course that is aannoying, because after every boot you have to do that ...
But at least a little change in hardware infrastructure solved the problem:
when connecting the webcam over an usb hub the problem didn´t appear again, the microphone port is correctly shown in the system preferences as "HD Webcam C525".
Hope it helps someone,
best regards ...