For some reason it doesn't want to play the sound for an AAC file though it is supposed to. Can anyone help me with this?
You have two options to choose from:
Switch the player and use something that's known, updated, one that supports all file formats. I recommend VLC Media Player for this job: http://vlc-media-player.software.informer.com/
Install a set of codecs on your PC and then use Free All-In-One Media Player to play the file again.
2.1. Download page: http://www.cccp-project.net/