No sound on XP

I am running a no brand computer with windows XP professional on it. It worked fine until a few months ago when I was notified of updating to Service pack 3. I could not get it to completely install and lost the sound at that time. When I tried to do a system restore it didn't seem to change anything. I then used the restore disc and had sound. Not leaving well enough alone I again tried to install SP3, whis time with the help of a microsoft tech. It still didn't install and this time the computer crashed.... According to the local tech my hard drive crashed. I had a new hard drive installed and he also put on service pack 3.... but there is no sound. The volume icon is also disabled and apparently the modem has become the default sound. I have several other sound devices listed but the computer has no location. Nor can the computer find the drivers to activate them (such as the multi media audio controller) Can you tell me what I can do or should I shell out more money to try to fix this problem. Or use it for target practice?