help with audio for XP

Hey i need some help.. im obviously a newbie so bare with me...

I think i need to install some sort of audio thing for my computer..
my sister was cleaning out my computer deleting things from the control panel and may have deleted audio stuff

now i cant hear anything from my computer, i went to check to see if the volume is on mute from the accessories-volume control and a screen popped up saying
"there are no active mixer devices available"

now i went to control panel, sound speech and audio devices and it says "No Audio Device" and i cant click anything...

so i need some help.. im probably gonna have to re install something, if i could be guided in the right direction that would be great


Thanks