Anoohilator wrote:1) Have you tried using other speakers? If same problem I'd try a new sound card; if it works, then problem with the speakers.
I agree on this. Usually, it's either your speakers have blown out (not literally, but they do break) or your sound card. Since from your post it sounds like your computer is 3+ years old, it's also very likely. I suggest one from Creative. Their cards are good quality.
(Remember: Be sure to ground yourself before you open the computer/touch the parts inside!)
I might even say your _wires_ but that's rarely the case.
2) Again I think it's just dodgy headphones - if your other ones work fine then it's the problem with the hardware
For some headphones, the sound tends to be softer. This is especially true for poor quality headphones and the ones that cover your ear. This is usually because they dont conform to the ear, and the foam covering lets soundwaves escape. (This does not apply to the studio ones that covers your ears AND around it. ie. headphones from BOSE.) The ones that go INTO your ear tend to be louder because they are closer to your eardrums, have a snugger fit, and prevent soundwaves from escaping.
Of course, your earbuds might not have a good fit, which could be the problem. The ones that go around your head have many different shapes of output (like, the shape of the part that goes around/into your ear), so I can't really offer any insight to that w/o further information.
There's also the problem poor wiring and bad speakers in the headphones. Or if the headphones are old, the jack might be worn down.
I may not be right, but this tends to happen to me so it might apply to you.