No sound or audio device?

Hello,

i have'nt had sound on my pc since a friend reformatted it mths ago...its saying theres no sound or audio device, i've read on the net that i need to reinstall sound device? any tips on how to do this im not all that clued up on pc's just use it for social purposes and music! im ok with installing things but but would'nt have a clue what im looking for or where to find it!!

if anyone can help either here or email it i'd really appriciate it. im on windows xp

cheers