Ok, try these things:
1. Open up your audio control panel software that came with your hardware (e.g., if you purchased an Asus motherboard, you need to go to the bottom-right of your taskbar and select Asus VIA HD Onboard Control Panel from the small icons). Then, find settings for audio configurations, and select 5.1 from there.
2. You need to change the settings in your media player to allow for surround sound (5.1). Find these settings in your media player and configure them to 5.1 output.
3. You need to play a file that is actually in the format of 'surround sound'. If you play your standard mp3 that only has 2 channels, it will only come from the front 2 speakers. So google 'free surround sound songs' or something like that, and play it in your media player.
4. If you can't find songs or your media player settings don't work, try playing a game... And in the audio settings change the setup to 5.1 surround...