no speakers or headphones are plugged in

Have you tried un-seating and re-seating the sound card in it's slot? Maybe remove it boot and shut down then install it again and re-boot? Have you looked for this card in your device manager ? Try this first right click on Computer then left click on Manage then left click on Device Manager then dbl left click on Sound controller.
Do you see the device there and if so try updating the driver there or even uninstalling it completely then re-booting and let Windows re-install it for you.

OK so device manager show the sound card and the sound card shows the correct driver. Left click on Start got to Control Panel and left click then left click on Hardware & Sound then click on Manage devices and tell me what it says. Then click on Adjust System Volume and tell me if the levels are muted or low while playing a cd. Thanks

Go through the previous steps to get to Hardware and Sound and then click on Adjust system Volume. Play with this setting while a cd or music files are playing and you should see the adjustable volume levels and with the volume levels set at middle setting you should also see a bouncing audio signal indicator.

Did you install the chipset drivers from AMD.com, you can't have sound if you don't install the chipset driver first

Even though you install over Vista you most likely still need to install drivers for Win 7, this is a common problem if you want the sound to work reinstall the chipset drivers