Windows XP Pro SP2 Sound Controls

I have Windows XP Pro SP2 installed in a desktop equiped with a Pentium III 850MHz CPU.
I created three users in this PC and all of the users belong to the Administrators group.
However there is only one user can hear sound from applications (Window Media Player, sound recorder, dictionary, etc) and the other two users can not hear anything from the same applications.

I would highly appreciate any help to solve this problem.

Many thanks,
le_vanhai@yahoo.com