I have just recently bought some harmon/kardon multimedia speakers. I pluegged them into the back of my CPU where the green hole was, then I plugged the left speaker into the right. I plugged an AC adapter into the speaker and then into the wall. The speakers are on and everything is fine, but no sound plays.

 

Whever I check my control panel it says I have no audio device. So I'm guessing I need to install them somehow. Any help?