Click on 'Audio' here:
http://www.dell.com/support/drivers/us/en/19/Product/inspiron-660
Then, alongside 'Cirrus Logic High-Definition Audio Driver'. click on 'Download file'.
Select 'Download & save'. Click 'Continue'.
Select 'Single-file download'. Click 'Continue'.
Click on 'Save file'
Where it says 'Save in', click on the downward-pointing arrowhead to the right of the box.
Click on 'Desktop'.
Click 'Save'.
Go to your desktop and you'll see the downloaded file there. Double-click on it to run it and reinstall the missing sound driver.
Then restart your computer. Hopefully you'll have sound back again.
You can now delete the installation file on your desktop. (Right-click on it and select 'Delete').
Chris