IDT Audio is a package that is delivered with the driver for your computer. To reinstall it first you need to remove it from the Add or Remove programs and Device Manager (Control Panel > System > Device manager). After you do this, reinstall the driver and the audio will work. Alternatively, make sure the audio service is running. Go to Start > Run > type services.msc and locate Windows Audio. Right click it and select Restart Service.
You can repair it via the Add or Remove Programs in Windows XP or Programs and Features in Windows Vista/7.