Hello mate.

You need to give us a bit more information on your system specs etc.

1) Are you doing the full install or the compact install?

2) Are you getting any error messages during the install process?

3) Have you ensured in the sound settings that these options are switched on?

4) What aircraft are you getting sound from?

It's possible that yor sound card is incompatible with the game (unlikely) or that there is some sort of install error.  Some people have fixed things by doing a full install and some by doing a compact install.

It may be worth downloading new sound drivers for your card, or DX9.  You could also try typing "dxdiag" in the Run section of the start menu and checking the sound options.

I hope that this helps.

Will