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Dive into the BIOS and see if there are any sound specific settings you need to change,
Make sure you've downloaded the latest drivers from the manufacturer's website (don't rely on the CD drivers or OS drivers - go straight to the source and get the latest, super-duper ones),
If on Windows, go to the Sound applet in Control Panel and make sure the volume is cranked up high there (it's an easy place to overlook when the system tray has its own volume control)
Good luck.