As far as I can tell there is no problem with the sounds on Lesson 9. If you ever have any problems with sounds, the first thing I would suggest is to close down your browser (all windows), restart it and try again.
If that doesn't work, could you please describe the problem in more detail. - Is it just lesson 9 that isn't working? Or have the sounds in other lessons also stopped working? - Is it *all* the sounds in Lesson 9, or just some of the sounds? - Do you get any error messages or any other indication that something is wrong, or do you just not hear any sound? - What operating system and web browser are you using (including version numbers)? - Is there any other useful information that you can think of?