A few minutes ago, I bought a headset from Wal-Mart, which is a Logitech USB headset with a microphone. I got home, plugged in the headset, and started up Garry's Mod, I went to the "Options" menu and checked to see if my headset was enabled and working. It worked just fine. I went on some Trouble in Terrorist Town server to check and see if it worked. I tried to speak into the microphone, but it didn't show that I was talking.
Help?