My new speakers are not working.

To make a long story short. My mother and I switched monitors when she bought her new computer. She didn't like that is was really big. (22inch widescreen) so I offered to switch my 17inch standard. I wanted it because I needed a new gaming monitor anyway. Well the sound works for my xbox. But when I connect it to my computer, there is no sound. I've done everything. Even been told that it's my sound card and that I needed to update it. Which I did, restarted my computer, and nothing still.

I'm running out of patience here. Can anyone help?