I found this possible solution for ya il copy and paste it in:
Fixing That Annoying Issue Mentioned In Other Reviews:
In the first review written for this headset, the author mentioned quite a perplexing issue that would drive anyone nuts. When using the mic, he would have to literally scream to get any input from it. I read that review before opening my package and had second thoughts about it, but then remembered the 14-day hassle free return policy. So I went ahead and opened it and plugged it into the nearest USB port [every side of my notebook. lol]. And I'll be dÃ…mned, the same problem. I tampered with all of the settings in control panel and in the volume properties, but to no avail. The headphones worked great, but the microphone seemed to be deaf. I had to yell into it just to get a small rise in the spectrum analyzer I used to test it. Before packing it back up and returning it, I Googled the issue to find a resolution. In the depths of a tech forum, my answer awaited.
To fix this annoying issue, and to save this product from a horrible one-star rating, you need to leave the headset plugged in. Without touching anything, run WINDOWS UPDATE and let it download all files that it presents you. Shouldn't take too long with broadband. After the updating, there was a new item in the 'audio devices' hardware, in control panel, called "C-Media USB Sound Device". Since then, the AC-850 has worked like a dream. Now, when I plug it in, a new volume panel opens when I double-click the volume icon.
Hope that helps mate
Taken from epinions.com