You can try the steps below and it should fix the problem.
A.Adjust the Audio Source Control Volume for the Microphone
1. Double-click the Volume icon in the system tray located in the bottom right side of the screen.
2. Click to uncheck any check marks in the boxes next to Mute to turn off muting for each volume control.
3. Click and drag each Volume Control slider to the top of the scale, if necessary.
4. Click Options and then click Properties.
5. Click to select the Recording radio button.
6. Click to check all the boxes listed under Show the following Volume controls:.
7. Verify the Mic Volume box is checked and click the OK button.
8. Click to uncheck the Mute box to turn off muting for the Mic Volume, if necessary.
9. Adjust the Mic Volume slider until it is near the top of the Volume Control scale.
10. Click Options and then click Exit to close the Volume Control window.
B. Test Sound Recording with the Dell Diagnostics
Follow the link below to run PSA
1. Ensure the system is powered off.
2. Press and hold the Fn key while system is powered off and press the power button to power the system on.
3. Release both buttons in 5-10 seconds.
4. The PSA diagnostics sequence begins. Tests will be performed automatically.
5. A message will display “where the color bars displayed”. Press ‘Y’ to continue testing.
6. Make note of any alert tones or error messages and forward it to us.
7. When a prompt comes to run more memory tests, Press “NO”.
8. Another test starts and chooses option “TEST SYSTEM”.
9. Please select “CUSTOM TEST” from the options.
10. Please locate “Audio”, click on that, and find “quick test only” (right top corner). Start test, by clicking on the start test button.
11. Make note of any alert tones or error messages and forward it to us.
Download and Install the Latest Audio Driver
Uninstall the Audio Driver
1. Click Start and then click Control Panel.
3. In the Control Panel window, double-click the System icon.
4. If present, click the Hardware tab.
5. Click Device Manager.
6. Click the plus (+) sign next to the Sound, video and game controllers category.
7. Right-click the name of the driver you want to uninstall and then click Uninstall or Remove.
Download and Install the Most Current Audio Driver Available
1. Go to the below mentioned link.
2. Locate Audio and click (+) sign next to it.
3. Click the Audio driver that you want to select. You may have to specify an installation method or operating system type.
4. Click Download Now in the File Name section.
5. Click Save. Using the Save In: drop-down menu, select My Documents, then click Save.
6. Click Open when the download completes.
7. Click Continue.
8. Click OK.
9. Click Yes in the Folder does not exist. Do you want to create it? Window.
10. Click OK, and follow the onscreen instructions.
Test the Microphone Using Windows® Sound Recorder
Click Start, click Programs (or All Programs), click Accessories, click Multimedia (or Entertainment), and then click Sound Recorder.
Click Record, and speak into the microphone. You will see the green waveform react to your voice.
To hear your recording, click the Play button and verify the volume level.