Could Anyone tell me what is wrong with sound

[Vasiltsov Vladimir]

Could Anyone tell me what is wrong with sound which should be played 
when new mail arrives in my mailbox.
Ok I'm using mozilla 0.9.9 on Win2k. It's IMAP and the checkbox 
"Edit->Preferences->Mail&Newsgroups->Play a sound when new mail arrives" 
is checked. There is no changes in prefs.js, when i check/uncheck this 
checkbox