Here are some steps you can take to try and fix a malfunctioning microphone on your computer:

1. Check the computer to ensure the microphone is connected correctly and is recognized by the computer
2. Ensure that the microphone volume is turned up to an adequate level and is not muted
3. Go to the Control Panel and select Sound. Check the Sound settings to ensure the microphone is selected as the recording input device
4. Update the sound drivers from the computer manufacturer's website or from the sound card manufacturer's website
5. Check that the microphone is not physically damaged
6. Run system troubleshooting to determine the exact problem with the microphone