BOOL PlaySound(
  LPCSTR pszSound, 
  HMODULE hmod,    
  DWORD fdwSound   
);

Parameters
pszSound
A string that specifies the sound to play. If this parameter is NULL, any currently playing waveform sound is stopped. To stop a non-waveform sound, specify SND_PURGE in the fdwSound parameter.
Three flags in fdwSound (SND_ALIAS, SND_FILENAME, and SND_RESOURCE) determine whether the name is interpreted as an alias for a system event, a filename, or a resource identifier. If none of these flags are specified, PlaySound searches the registry or the WIN.INI file for an association with the specified sound name. If an association is found, the sound event is played. If no association is found in the registry, the name is interpreted as a filename.

pszSound에 NULL을 넣으면 현재 플레이중인 사운드가 멈춘다네요~ ^^