Have you tried switching it on? Probably you just need to enable the mic-boost function.
If you were any more vague, you wouldn't exist.
Perhaps we can help - if we have some information?
Try reading:
http://www.linuxquestions.org/linux/...Ask_a_Question
Here are some pointers:
1. state your problem in the title
2. edit your profile to show your distribution and location
3. tell us your distribution - which "linux" is this?
4. how are you trying to use the microphone?
5. in what way is it "not working"? What are the symptoms?
But while I have your attention - open a terminal and enter "lspci".
You'll get a big list of text - look for the line that talks about your sound-card, copy it, and paste it to your reply.
Look for anything called "volume control" on your gui someplace or in a menu. Often you can rt-click the entry or get some sort of settings dialog up. Look through that.