Not sure how deep into things you have gotten...
What make and model mic are you using? USB, 1/8" (3.5 mm) connector plug?
Does the mic work on other computers? Do other mics work on your computer? See if problem follows the mic or stays with the computer. Be sure that the microphone is in the correct port: e.g., sound card versus motherboard.
Have you right-clicked the speaker icon (lower right screen corner) and selected "Recording devices"?
There are a number of configuration settings available with any given recording device: you need to work through the various windows, tabs, and properties associated with any given recording device.
Explore the settings first, then make a change (one at time) that seems viable. Keep notes on what you do and where you did it should a reversile be necessary.