The term CARD is frequently mis-used. A CARD is installed in a mboard slot, or on a header on the mboard, and is removable. A USB device such as a sound adapter isn't a CARD. An onboard sound adapter, an onboard network adapter, onboard video, is NOT a CARD.
I can't think of any reason installing SP3 updates would cause your sound that was working before to stop working, unless something went wrong, which is possible when you install SP3 updates when you already have additional programs installed that did not come with Windows when you installed the SP3 updates. If that's not working right, there are probably other things that aren't working right.
E.g. the SP3 updates often do not install properly if you did not un-install anti-malware software before you installed it, or you at least disabled it's resident module(s) that run all the time. e.g. You MUST un-install Norton Products, otherwise there will be things wrong.
If you install SP3 updates right after Windows has been installed, or at least before a lot of software that didn't come with Windows has been installed, you usually have zero problems after installing them.
If your sound adapter (chipset) is onboard, which is quite common, the 1/8" ports (jacks) for it are in the same area I/O area all the other ports built into the mboard are in on the back of the desktop computer; laptops always have onboard sound. The specs for your computer model on the Gateway site tell you which sound chipset that has, the name of it, and the drivers for it are in the doiwnloads for your model.
But if the sound was working before, it should still work.
If your sound adapter (chipset) is on a card in a mboard slot on a desktop computer, the 1/8" jacks for it are on a plate in a slot space, not in the main I/O area. You have to find the model of the card on the card itself in order to find the drivers for it.
Windows can support more than one sound adapter, but you can only use one at a time in Windows. The last one you installed the drivers for becomes the default sound adapter in Windows, but you can change that in Control Panel.
If you have both onboard sound and a card in a slot, plugging into the jacks for the last one you installed drivers for should work fine.
"I have tried system restore, but am unable to
restore to any previous point"
They may be wiped when you install SP3 updates, or they may still be there but can't be loaded because having the SP3 updates loaded makes them un-usable.
"This implies I have a Realteck high definition
audio sound card, which is what shows up in my device
manager, but no sound card is detected in the control panel
You could try
- download the drivers for the onboard sound if you are using that from the Gateway web site.
- uninstall any entries for like named sound drivers in Add/Remove Programs
- do NOT install the drivers for the sound while booting the computer, when Windows detects the sound adapter. Cancel that, continue to the desktop.
- install the proper sound drivers and related software ("sound driver" downloads almost always have related software included in the installation) . Sometimes they extract themselves and install themselves. Sometimes you must extract them to somewhere, then run a Setup program.
Reboot if you were not prompted to - you should have sound after the next reboot.
If that doesn't work, do you have or can you borrow a regular XP CD preferably with at least SP1 updates included on it?? If you do, a Repair" Setup procedure may fix your problem(s), without you losing any personal data you have added to the Windows partition.
OR - do you have the Gateway Recovery disk(s) for your model that may have come with it when it was new - sometimes one is actually a slightly modified XP CD (at least, that's often the case for Dell, HP, and Compaq systems).