Head set w/mic. Having problems

The problem is I can't get the mic to work. I can hear sound but I can't talk to anyone (when playing cs.). I'm using a splitter and that one is hook up to my xfi sound card and the other end of it I have my headset hooked up which has 2 male jacks, 1 for the sound and the other one for the mic. Any ideas what am I doing wrong? I when into windows volume control to make sure nothing was muted.The brand that I have is cyber acoustics. My stand alone mic works fine. All I do is just plug it in and it works. I don't know why i'm having so much problems with this headset mic combo. I have a regular headphones which works fine with my stand alone mic. The reason I bought the head set w/mic is because the stand alone mic picks up other sounds which makes it hard for other players to understand me. Any help would be great thanks.