When I connect my computer to my home theatre surround sound system, my speakers and sub, buzz loudly?

If the static is coming through only one speaker, check the speaker wire first. Make sure that you aren't running it next to any power cables since speaker wire can pick up electric fields and create that static noise you are talking about. If everything looks fine, swap the speakers. If the static comes from the same speaker, you probably need to replace it. If the static stays on the same side, you've probably got a problem with the Y-splitter. Check to make sure that the cable is securely connected to the computer. This may sound trivial, but I've knocked mine loose a few times and had the same problem. If the static is coming from both speakers, check to see if the Y-splitter is running next to any power cables. Again, these splitters tend to pick up electronic fields and give off a static noise as a side effect. If that doesn't change anything, replace the y-spitter with one that has gold connectors and looks thicker. This will mean that you have a better connection with more insulation and the static should go away. I don't think the problem is with the computer because swapping from the headphone jack to the sound card didn't do anything. There's always a chance that your sound card is bad, but I've had this problem before and I was able to fix it using the methods above. Besides, a new Y adapter is a lot cheaper than a new sound card. It's worth checking out.

also could be noise off the computer ie the harddrive and fans and the speakers have to take in any interference, and you want to go from mini jack to rca if connecting to your stereo