Since you said
We have downloaded several sound drivers, but none seem compatable with the sound hardware that this motherboard has.
It sounds like you have onboard sound (built into your motherboard) instead of having a separate sound card. However make sure this is the case. See what it has listed for your sound card. There are instructions for opening Device Manager
***here***.
If something like Realtek or AC97 is listed in Device Manager under "Sound, video and game controllers," you have onboard sound. However if the computer is 1995-2000 vintage, it may have different onboard sound. It might be better to check where your speakers are plugged in, because it's possible the computer has both onboard sound and a sound card, but you're not using the onboard (which used to be horrible in older computers). In
***this example***, the green area is where the onboard sound is, and if the computer had had a sound card, the plugs would have been down in the red area or even farther down. An example with a separate sound card is
***here***.
If you have onboard sound on a custom built computer, you'd look for drivers on the website of the motherboard manufacturer. You have to know what model motherboard is in the computer.
However if it is a name brand computer, like a Dell or HP, you'd look for drivers on the website of the computer -- and you'd need the model number of your computer. Even when a manufacturer (like Dell) has separate sound cards in the computer, the version of the card they sell may be different from the retail version -- so you should get your drivers from the computer manufacturer.
If the problem isn't the drivers or the sound being muted (by a game or some other glitch), the sound card may have gone kaput and you may have to buy a new sound card for the computer. If you have to do that, you'd probably be better off buying an old sound card from before year 2000 that should have good drivers for Windows 98.
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Lot of stuff -- much of it which you may not understand -- but the long and short of it is that without more information about your computer, whether it's using a separate sound card or onboard sound, etc., we can't find drivers for you.