call of duty sound problem it wont start the game

please help me, i think my sound card is sompatible but when i try to start the game it says (in singleplayer) 17 sound files missing or bad or something like that and when i start multiplayer it says the same like 20 sound files missing. i have bought the game 2day and its legal. please help me.

my system is a 1.8mhz pentium 4 with 64 mb geforce video card