Is that a Dell PC which needs the Windows 7 Soundmax driver for its sound chip ?
I had a similar problem when upgrading to Windows 7 from XP on a Dell Optiplex GX 520/620
I Googled for the driver and found lots of rubbish trying to sell a driver update program
but I found a reference to the Dell update site for a Windows XP + Vista driver
which also works under Windows 7