Sounds like a message from Microsoft Windows Media Player.
Could be that another program has control of the sound card or the sound
card is not functioning. Make sure you close any other applications
that may be using your sound card.
You may have another piece of hardware that is conflicting
with your sound card. You can check this by opening the 'Control
Panel' and selecting the 'System' icon. Click on the 'Device
Manager' tab. Under the 'Sound, Video and Game controllers' heading
it will list all of your installed devices. If any have a red
exclamation point in front of them, the device is disabled because it is
conflicting with another device. If this is the case you will
have to open the device and change its settings to a resource that no
other device is using. Or you can open the device that the sound
device is conflicting with and change its resources. If you have
just installed new hardware, the new hardware may have taken the
resources the sound card uses.
It could also be that the sound device drivers were not
properly set up to begin with. If the sound on your PC never worked
this may be the case. You will need to get the latest drivers for
your sound card from you manufactures web site and run the Add/Remove
Hardware program under the Control Panel.