If you are plugging into the "line in" on your computer, make sure in whatever your recording with, or playing through, has it's "input" and "output" set up properly.

First question; what are you trying to do? Are you just playing through your computer with some sort of effects program, or are you using some type of recording software? This will help clarify how to make sure you get the sound to come out and get what you need.

Let me know and we will take it from there. Happy to help :D