I am an ex-Gateway tech and am very familiar with the hardware from that time period.
First, what kind of sound card is it? My guess is that is either a SoundBlaster Live! or an Ensoniq PCI 1373. You can verify that in device manager.
Also, what kind of speakers are they? Given your description of the issue, I would hazard a guess that they are either Boston Acoustics BA635 or BA735. However, I could be dead wrong :).
Anyhow, post what models of each you have. I have several ideas of what could be the issue, but would need that extra information so I could narrow down the issue for you.
Actually, here are links to the specific issues I was thinking about:
Just run through these and tell us if it works, and if not, then post what kind of sound hardware you have.
http://support.gateway.com/s/issues/134527880.shtml
http://support.gateway.com/s/issues/137434110.shtml
http://support.gateway.com/s/issues/137433711.shtml
The last article mentions the BA745 and BA7800, but it also applies to the BA635 and to the BA735 (if the BA735 is being run with the analog cable - the analog cord is the cord with the green plug going into the computer. The digital cord, IIRC, either has a black plug or a white plug going into the computer).
Finally, as a last resort, grab another set of speakers from a friend and try them. If they work, it’s a speaker issue. If they don’t, it’s a sound card issue.
critter42