How to Test a Line-In Jack on a Computer. The "Line In" audio jack on your computer enables you to connect a microphone or other audio output device with a 1/8-inch miniature plug to your computer.

If you need to connect surround sound to your computer, all that is required is that your sound card has surround sound ports.

Ran trouble shooter. Heard test sound. Sound works. Shut down computer. Fire it up, no sound. WTF??? I think it has the usual Dell onboard sound, not a separate card.