I no longer have sound. When I click on the sound icon, I see "VOLUME 0, speakers, IDT High Definition Audio CODEC." When I right click and select "Open Volume Mixer," I get the error box that reads, "No audio device installed." When I look in the device manager (control panel | device manager | Sound, video and game controllers), the IDT High Definition Audio CODEC device indicates that it is working properly and is enabled.

Laptop is Dell Latitude E6400. OS is Windows Vista Service Pack 1. Thanks!