please answer the following questions and follow instructions accordinlgy:
1. did it ever work? what changed since?, if something change try to use system restore to go back to the time prior the changes
2. did you just installed the chat application? skype?msn messenger? yahoo messenger? if you just install the application where you are trying to use the mic. you need to configure your mic before you can use it. usually under tools or settings you will find sound devices, some computer may have more than one source of input sound (mic) so go into those settings and look for a way to set your mic as the source and test to ensure it is working. the configuration procedures may differ among applications.
3. did it work and stop working all of a sudden and system restore won't get it working again?? you may have a driver issue, first try to reinstall the driver for that you need to do into device manager, found the sound devices, select the device with a yellow ? or ! and attempt to uninstall the driver, then restart your computer, the driver will reinstall by itself, then go into the chat application and reconfigure your input device and test.
on some ocations you may have to look for a new driver to solve your problem for that you need to go into the manufacturer's website, look the model of your number up and look for the a possible new update for your sound device driver and installed as per manufacturer's instructions. find the drivers need for your system
hereprovide more details as noted above and if possible we will try to assist further.