Hope you would able to help me with this...

Hello! I'm having trouble with my audio device...I guess I accidentally did something wrong when I used to fixed my PC trying to remove a virus in it. I succeed in removing the virus and restore my system however as it finished the restoration process, i found out that I lost the sounds of my computer. I notice that the icon for master volume located beside the clock seems to be missing. I tried to see it at the entertainment sub menu but whenever i tried to click it, it says that i need to have a mixer? (i really don't get it). will you please help me with this? i also tried to look at the device manager and all seems are working properly except for the yellow question mark-> Multimedia controller? (i forgot the whole term) i'm not quite sure if this has something to do with my problem. By the way, I'm using a desktop computer, Windows XP.. I would really appreciate your help. thanks.