Go to Control Panel \ Sound and Audio devices \ Voice tab \ Voice recording, Default device: make a note of the driver name and audio input, and check on the dropdown windows if it is the only driver available, if there is another driver, try that one. If there is no other, click on the Volume bar and check your Mic Volume..
If this doesn't work, check your Device Manager: Start \ Run \ Type: Devmgmt.msc and hit Enter \ and under Sound, video and game controllers, check the Driver named the same as the one you made a note of (Control Panel \ Voice \ Default device).
Is that driver marked with any symbol? (meaning it's disabled or corrupted)
If the driver is not marked;
1. you may need to update it,
2. your microphone may be damaged or incorrectly installed.
3. Your computer may have front and rear audio connectors, try connecting the mic on the opposite side of the case (blue jack audio input connector).