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(A). Try to connect a microphone to your computer in this way.
After you've plugged a microphone into a microphone jack on your computer and turned it on (if the microphone has an on button), follow these steps.
1.Open Sound by clicking the Start button , and then clicking Control Panel. In the search box, type sound, and then click Sound.
2.Click the Recording tab, click Microphone, and then click Properties.
3.Click the Levels tab and make sure the Mute button looks like this . If the button looks like this , click it to turn on sound for this connection, and then click Apply.
4.(Optional) To listen to microphone sounds through your speakers or headphones, click the Listen tab, click the Listen to this device check box, and then click OK.
"Connect a microphone, music player, or other audio device to your computer"
(B). Check the lights if it glows when the speakers are plugged in.
(C). Try connecting the headphones to the different slot (Front) or to a different computer and check.
(D). It can be an issue with the slot itself where in the device is not getting recognized because of the hardware fault.
Hope it helps
Thanks and regards
Dinesh-Microsoft Support
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