No sound and audio device

Hello,

please help me 'coz it's my big problem as of today.

We just watched youtube videos last night and as I opened my pc this morning,
my sound and audio devices are not working!!!

Realtek is still installed on my pc. my OS is Windows XP.
I already restore my pc and updated the realtek and also my audio codec in System hardware
but still, it's not working!!!

please please please... i need your help!