First off, I would highly suggest you try running windows updates, that sometimes pickups the missing driver and fixes the issue. However, if that dosent work I would suggest you see if you can find the cd's or dvd's that came with your pc. One of the should most likely be a cd with all of drivers on it. If you have that cd you should be easily able to install the drivers you need.
If none of those ideas work, we will need the exact manufactor and model of the pc and we can see if we can help you locate the proper drivers for your sound card.
I can't help ya there, I don believe I have ever tried to backup my drivers, never found the need to do it. I always either use the cds that came with my parts, or 99% windows update pickups everything i need.