It could be the mic, the mic jake, or the OS install. The first step is to identify the location of the problem. The odds are that it's not software, so long as all your mixer settings are okay, though it could be.
Here's one way to do it: Test the mic with another computer. If it doesn't work, it's the mic. If it works in another computer, it's not the mic.
Boot the problem computer to a Live CD of something else and test again. If it works, it's not the mic or the mic jack or an internal connection (I had a wire to the external speaker jack in a desktop work loose once), so it's likely the OS. If it still doesn't work at this point, it's almost certainly hardware.
If you get this far, obtain a known-good mic from somewhere and test with it. That will give you near certainty as to whether it's the mic, the hardware, or the OS install.
Last edited by frankbell; 12-28-2015 at 10:12 PM.