double click the speaker icon, which should be on the lower right hand side of the desktop screen
if you do not see the speaker icon, you may see an arrow pointing up, in the lower right hand of your desktop screen...click on the arrow, then click on customize, then set the speaker icon to: "show icon and notifications" also in this menu, you may locate your audio manager icon, set this icon to: "show icons and notifications"
after you double click the speaker icon, you should see audio settings software.
check through the audio manager for the microphone settings, and look at the audio mixer, check to see that the mic is enabled...
if you are not able to find an audio manager, it may have been deleted
go to the manufacturer's dell website and download the latest audio drivers, look up your computer by the service tag number, delete the current audio software and drivers, turn off your anti virus and firewall, reinstall the audio software or drivers, restart, turn the anti virus and firewall back on.
if you upgraded the dell to windows 7, there may be other drivers for the computer offered on the dell website, for windows 7, to update the computer.
if you are running multiple security programs, turn them all off or delete them first.