If you add a wav file, make sure you add its path to the string table (I think this might be automatically enforced, but I forget). Also, if the wav is in a folder in the archive, you need to use double-backslashes to specify the path to it. For example, if your sound is in staredit\wav\sound.wav, your trigger needs to look like:
PlayWAV("staredit\\wav\\sound.wav");