If your computer came with a motherboard disc the sound drivers could be on it
you might have to uninstall then reinstall both the sound drivers and the sound card make sure you have both of these devices backed up to a disc before uninstalling
a yellow? question mark means you need to install/update driver to do this
right click to install driver also
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 select 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)

hope this helps