The first thing you must do is to plug your headset in. (Note: If you have a laptop you did not need to do the next two steps.)
Cords (if USB go to next step):Put the Mic cord in the Mic port and the Audio cord in the Audio port (these are normally on the front of your pc).
USB (if you just did cords, skip): Plug USB into a USB port (recommend USB 2.0 port). Install any drivers needed to operate with that headset.
Open Windows Start menu, then select Control Panel, then select Sounds and Audio Devices.
In Sounds and Audio Device Properties, select the Voice tab.
Click the Test Hardware button.
Go through the steps in the Sound Hardware Test Wizard as prompted.
After finished with "Sound Hardware Test Wizard", go into Combat Arms.
In Combat Arms, go to Options>Sound Tab>Microphone>and select your headset device.
Press Test i think? to make sure you can hear yourself.
Now you should be good to go