If you are experiencing problems with sound not playing back for audio files or in video, or video is not playing, then the most likely reason is that there are codec problems on your system.
Please do this as the first resort:
UPDATE YOUR COMPUTER'S CODEC
Download and install the following codec pack (very commonly used and widely known FFDSHOW codec pack) to see if it helps:
During setup, there will be a page called Select Additional Tasks, and you will see Decode the following video formats with ffdshow and Decode the following audio formats with ffdshow. Make sure that option is checked.
After finishing installation, no need to do anything else. Just reboot Windows and give it a try (or may not need to reboot Windows, but at least restart your BrillKids software).