Another possiblity is that your sound driver is corrupted in some way.
You can test this by updating to the latest drivers. Go to your computer manufacturer's website and search for the latest drivers for your computer.
Alternativly, you can try using the windows Generic driver instead:
Step 1: Determine what driver your computer is currently using: Hover your mouse over the volume icon in taskbar system tray.
A balloon should appear, showing information about your sound system: Master Volume Level, Device Type, and the Driver you are using.
If the last line says "Realtek High Definition Audio", you are using the Realtek driver and will need to switch to the Generic Windows driver.
If the Balloon instead says something like "High Definition Audio Device", you are already using the Generic Driver.
Step 2: Create a Restore Point: If you change your mind and want the Realtek Driver back, you can use this Restore Point to undo your changes. There is a good tutorial on how to create a restore point here.
Step 3: Uninstall & Delete the Realtek Driver:
Open the Control panel (Start> Control Panel).
Click on "Hardware and Sound".
Click on "Device Manager". You will need to have an Administrator's Account to access this.
A list of all devices on Computer should appear, as shown below:
Expand the "Sound, video and game controllers" category.
The Realtek Driver should be listed as shown above.
Right-click on the Realtek entry and choose "Uninstall" from the menu.
A dialog box like the one shown below will appear:
Make sure that the box next to "Delete Driver Software for this Device" is checked. This is important. If you don't delete the Realtek Driver, Windows will simply reinstall it. (If you wish to uninstall and reinstall the Realtek driver for troubleshooting
purposes, uncheck the box.)
Click Ok.
Windows will prompt you to restart your computer. Do so.
Step 4: Installing the Generic Driver:
When your computer starts back up, once you've logged in, you may receive an error message stating that the Audio Control Panel Applet is no longer working. Ignore it.
After a few moments, Windows should begin automatically installing the driver for your "new" device.
When it is finished, hover your mouse over the system tray icon again and you should now see "High Definition Audio Device" in the Driver line.
If Windows does not automatically install the driver, return to the Device Manager, right-click on any list entry, and choose "Scan for Hardware". Windows should then find the Audio Device and automatically install the Generic Driver for it.
If you change your mind or find that this does not solve your problem, you can always use the restore point you made to return to the Realtek Driver. Or you can reinstall the Realtek Driver using the Driver CD that came with your computer.
Best Wishes,
BookwormDragon