To troubleshoot why a linked video isn’t playing in PowerPoint, you can try the following steps:

1. Check that the source file is in the correct format
2. Ensure the source file is in the same folder as the PowerPoint presentation
3. Make sure the video can be played back using Windows Media Player or VLC
4. Check that the video player plug-in and codecs are installed
5. Try using an alternate media player, such as QuickTime