Check that you haven't accidentally clicked the microphone mute button on your device or headset in skype.
1. Do this:Click your "Tools" tap then click "Option" then on Audio Setting make sure you click on you current mic and then "save".
2. Inside Control Panel, go to Sound -> Communications. That tab says: Windows can automatically adjust the volume of different sounds when you are using your PC to place or receive telephone calls. When Windows detects communications activity and answer "Do nothing" instead of the default "Reduce by 80%".