Does the mic work on other devices? On my laptop only my old Logitech's mic died, but on my android phone it didn't detect the headset at all. If it also doesn't work on other devices / your phone doesn't detect the connection, you should ask for a replacement. If it does work on other devices, I would like you to take the following steps. This is similar to the answer of viveknayyar007, but there's a little difference.
1. Go to settings (Windows key + I)
2. Go to privacy
3. From here, go to the Microphone tab
4. Click the change button, and make sure the option is on
Another trick can be this:
1. Right click your sound icon & click sounds
2. Click on recording
3. Double click your mic & go to advanced
4. Now try different sample rates, if multiple ones are working pick the highest one for the best mic quality