I connected a pair of Bose Companion 2 speakers to my PC but not getting any sound.

If your computer came with a motherboard disc the sound drivers could be on it
click start control panel administrive tools computer management device manager scroll to sound,video and game controllers you might see a yellow question mark? Right click to reinstall drivers
click start control panel sounds and audio,volume,advanced,speakers make sure you have selected the
(((appropriate speakers))) also audio you will find 3 drop down lists make sure you have the correct settings there
also
click start control panel sounds and audio devices you can adjust the volume there also select speaker volume you can change your settings there you can also tick in the box place icon in taskbar
if his does not fix the problem

have you tried this control panel sounds and audio,volume,advanced,speakers select the appropriate speakers from the drop down list or navigate to the device manager scroll to system devices + to expand,system speaker right click properties then select use this device (enable) also you might check
the speakers plug/outlet is usually at the back of the computer you will have to open up the computer to check the lead attached to the rear of the input plug make sure the connection is good
try cleaning your computer of dust using a fine air blower from a compressor making VERY sure that there is no MOISTURE in the air line specifically around the sound card and the CPU central processing unit dust causes static to build up in a computer
hope this helps