I think your easiest solution Lona is going to be to get a PCI sound card.Then you can disable the onboard sound and use that one instead.You can buy one sufficient for your needs quite cheaply
The other way is to see what motherboard you have then we can possibly see what the specifications are for it and hopefuly find out exactly what your options are.
To save you pulling your PC to bits if you install a program like Si Soft Sandra ( I think you said you may have it somewhere
) that will tell you what your motherboard make and model is