There are a number of common problems related to audio or video sequences. These include the following:
- Sound turned down or muted on computer system.
- Speakers or headphones unplugged or not switched on.
- No soundcard present.
- Soundcard driver corrupt – re-install Driver.
- Flash software failure – Install latest version of Flash.
- The video may have been encoded with a codec not present on your computer – install correct codec.
- Audio and video being out of time (also known as out of sync).
There are many other problems that may occur, please check the Audio FAQ at http://manual.audacityteam.org/o/man/faq_recording_troubleshooting.html
and the Video FAQ at http://wiki.videolan.org/Common_Problems