[UserNameGoesHere]

It could just be (and likely is) some kind of configuration problem (either system-wide or in your individual program you are trying to use). I'm surprised no one has mentioned this yet.

You'll have to go playing around with a bunch of stuff though. There's not really one "fix" to this as it differs widely.

Some things you can try:
Adjusting various volume controls
Changing which jack is the one your program takes input from -- sometimes it matters.
Disabling onboard audio if you have a sound card (if you don't have one, leave it be)
Updating audio drivers
Just playing around with whatever audio options are available to you (differs widely)

If the jack itself is going bad (doubtful) you could try putting it in almost, but not quite, all the way -- there may be some point at which it kind of works but past that it doesn't.