The only reason I can see for it not working is it can't find ding.Wav. I have run it on my system and it works fine.
Make sure the file ding.Wav is in the same directory as the class file and if you are running on a case sensitive OS that the case is correct. You should also try running the wav file directly from the OS to make sure it is outputting an audible sound.
Try adding the following lines to your code just before you create the audio clip
and then run your applet. You should see the print out in the applet console and it will tell you if the sound file is visible.
File f = new File(getCodeBase().getFile(), "ding.Wav");
System.out.println(f+", Exists = "+f.exists());