What the problem usually is, other than possibly the software not installing correctly for the program that uses the mic, is there may be several applications on a computer that can mute the mic, and one of those is set to mute it. E.g. a speech to text program. Sometimes it's software is faulty and the mic remains muted even when you are not actively using the program.
You could also check Control Panel - Sounds and Audio Devices Properties - Voice - Voice Recording to make sure the mic is selected and being detected.
If you have more than one mic (e.g. some web cams, some speaker sets have built in ones) make sure the mic you want to use is selected there, and in the properties or settings of the program you are trying to get the mic to work in.
If your mic is into a port on the front of the computer or elsewhere and not plugged into the mic port in your onboard sound ports or the mic port in your sound card, the port may not be wired correctly - try the onboard or sound card mic port.
The mic must be a type that will with your computer's sound - if it doesn't have enough output, you won't be able to hear it at any volume. Sometimes there is a mic boost setting you can turn on in the Windows mixer - Options - Properties, or in a separate mixer for the sound.