moving this to tech help.
To answer your question, neither steam nor the servers have anything to do with your mic functionality. You need to ensure that your audio drivers are properly installed. And depending on your operating system (XP or older) you could need additional drivers specifically for your headset.
-Blue
There is the possibility that Steam doesn't see his headset as a audio device... I had that happen with a USB Headset my friend gave me after my cat knocked my plantronics headset that I had a few years back off my desk and broke them.