When connecting 5.1 channel speakers to your system, it can be tricky getting them configured properly.
Before continuing, check to see that your connections are correct. Do all your satellite speakers plug into your Subwoofer/Bass speaker with a single analog plug into the green audio out? Or are you using multiple analog cables? See this article for additional assistance on connecting audio devices to your PC.
On some systems with Realtek onboard audio where there are only 3 analog audio ports on the rear of the PC, a number of settings must be checked on the system to get audio from all ports.
To address this: