I don't have audio on the web... example: I can't hear nothing when I play videos on "you tube"

I'm using Kubuntu 9.10... I can listen music with amarok and see video with audio... but on Internet I can't hear nothing...
I update karmic koala every day.

ProblemType: Bug
Architecture: i386
Date: Sun Dec 20 15:34:15 2009
DistroRelease: Ubuntu 9.10
ExecutablePath: /usr/bin/kdeinit4
InstallationMedia: Kubuntu 9.10 "Karmic Koala" - Release i386 (20091028.5)
NonfreeKernelModules: nvidia
Package: kdelibs-bin 4:4.3.2-0ubuntu7.2
ProcEnviron:
 LANG=it_IT.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-16.53-generic
SourcePackage: kde4libs
Uname: Linux 2.6.31-16-generic i686
XsessionErrors:
 (<unknown>:2175): Gdk-CRITICAL **: gdk_window_get_origin: assertion `GDK_IS_WINDOW (window)' failed
 (<unknown>:2175): Gdk-CRITICAL **: gdk_window_get_origin: assertion `GDK_IS_WINDOW (window)' failed
 (<unknown>:2175): Gdk-CRITICAL **: gdk_window_get_origin: assertion `GDK_IS_WINDOW (window)' failed