1. Open Control Panel - Sound and Audio Devices.
2. On the Volume tab check if "Place volume icon in the tasbar" is grey out.
3. Click the Audio tab and check Sound Playback "Defualt Device". Is it None?
4. If that is so, then Right-click on My Computer and choose Properties.
Click Hardware tab and then Device Manager.
5. Note if any device has an exclamation sign with yellow color. It should
be "Other Devices" or "PCI Device" or your sound Card name e.g. "Realtek AC
'97".
In that case you need to reinstall your Sound Drivers from your Motherboard
or Sound Card CD, if you have it. Otherwise, you can download the drivers
from Manufacturer's website. See your Motherboard or Sound Card manual for
further download details.
Hope this help, let us know!