Please help me that i lost sound files for fsx

Try running the integrity verification process for FSX through Steam.  You can do this by going to FSX SE in you're Steam library and clicking on the little gear shaped icon in the upper right, then select properties, click on local files and there you'll see a button labeled Verify Integrity of Game FIles.  Click that and let it run until it's finished.  This process should repace any missing game files.  If that doesn't work than you're only option is to reinstall the game.