Either go through the paperwork that you (assumably) got with the computer or open the case, unplug the power, demagnetize your hands and move out the soundcard. See if there's a name or a number printed on it. Or perhaps a sticker.
Unless you have an onboard soundcard, in which case you could perhaps see what kind of soundcard it is by inspecting your mainboard or going through the BIOS.
Did the person who sold/gave you that PC not supply you with any CD's or diskettes you haven't used yet? If so, please inspect them.
This might help solve your sound problem, I donot know if your aoxdxipl.ax error has to do with your soundcard.
Also, when and how did your sound degrade?