sound problem with windows 7

I have windows 7 ultimate x32. most times when i start my laptop for the first time i get the start-up sound. in the icon in the system tray shows tha sound works ok... but when i try to play a sound file, or watch a video in youtube for example, i hear nothing. I also get the shutdown sound.

Anyone has any idea what's going on? what can I do to fix this?

Thanks

hey try dis file and solve ur sound problem .............
DuckLoad.com · Easy streaming