Why Can\'t I Get 5.1 Sound On My Win 7 System! HELP!

Have you installed the latest sound drivers? What sound card do you have?

so you going to Control Panel >Sound, in Playback tab clicking on your speaker and then clicking on Configure but there is no choose there to switch to 5.1 ???

lol, we need to know way more information:
What sound card
What cables used for audio? (analogue discrete 5.1 output? SPDIF wire? SPDIF light? HDMI? Ethernet?)
What type of amp/receiver is being used (if in a home theater setting)? What type of speaker system is being used (if a PC setting)
7 home? starter (no surround support)? pro? 32bit? 64bit?
Have you installed the proper/latest sound drivers (audio drivers are super picky in Vista/7)
Have you selected the proper audio device? Vista and 7 can do multiple audio devices much simpler than XP and previous versions, which is great for people like me, but can be a real thorn in the side for those who are not use to sound management. Also, if you recently installed a video card with an HDMI output, be aware that win7 will almost always select that as the default device, and you will have to change it back to your sound card if you want to use that.
Have you tried disabling the sound management software that came with the device (the software, not the driver), and using the windows sound manager instead?
Have you selected a proper bit depth and sample rate that matches your audio system? Most amps and devices are limited to 96KHz (or less) and 16bit, only newer devices (or high end old devices) can do 24bit audio, and super high rates like 196KHz. Even mine is 96KHz/24bit, but when it is digital it is pretty damn nice   even when compared to good analogue 196KHz/24bit