PPT not playing sound for avi file

Hi,

I have a ppt presentation that I have developed on my PC (Windows XP,
Powerpoint 2002). In the presentation I play .avi files.

To get the files to work I have placed them as objects rather than going
through the InsertMovies function.

I followed the following instructions from the Powerpoint help file to
insert the movies.

"Display the slide you want the movie on in PowerPoint, and on the Insert
menu, click Object.
Under Object Type, click Media Clip, and make sure Create new is selected.
If you want the movie to display as an icon, select the Display as icon
check box.
Click OK.
On the Insert Clip menu in Windows Media Player, click Video for Windows.
In the Files of type list, select All Files, select the file, and then click
Open.
To play it, click the Play button just below the menu bar, on the upper
left;
To insert it onto your slide, click outside the movie frame. "

Everything works fine on the PC. The movie clips open and play perfectly.

Today I copied the presentation and .avi files to my laptop (Windows XP
Home, PowerPoint 2002) (where I will be playing the files through a
data-projector). When I play the presentation, the movie plays but there is
no sound. After searching around on the web for a while I found the
"Microsoft PowerPoint and Multimedia" FAQ by the MS PowerPoint MVP team. I
followed the instructions in that FAQ and found that the problem is in my
MCI installation. I had a look at the registry settings as per the
instructions in the FAQ and there was nothing different.

Does anyone know how I restore or fix this MCI? I have had a look on the
Microsoft Web-site but am not finding anything of help there.

Thanks in advance

Simon