Okay, that's a bit more to work on. HD audio usually has a jack detection feature, and can often be configured to route different audio to different spots. If you open your audio control panel in Control Panel, it might look something like this:
Mine is a Realtek driver
. I can separate the Mic jacks, or tie them together if I want to, or I can disable either one. I don't use my rear one, so I have it turned off. You should have something similar in your machine. Snoop around in your Control Panel and have a look. It's probably working fine, just disabled right now.
Post back if you still have some trouble.