computer microphone doesn't work

Hey guys. I'm trying to get my microphone on my computer to work but it just won't detect anything. Sound on my computer is fully functional, and I know the microphone is too because I went on my brother's laptop and it can record my voice just fine. It has something to do with my computer. I looked in device manager to see if there is anything with a "?" but there isn't; so everything is installed properly I assume?

I tried to uninstall and reinstall the driver but I'm not sure if I am doing it right. Any clue on what is going on here? Or what I should do for that matter..

thanks