Based on dozens-to-hundreds of sync messages (you DID use the forum search before asking?) I am going to guess you are trying to edit a view only file
This is aimed at Premiere Pro, but may help
A link with many ideas about computer setup http://forums.adobe.com/thread/436215?tstart=0
Work through all of the steps (ideas) listed at http://ppro.wikia.com/wiki/Troubleshooting
If your problem isn't fixed after you follow all of the steps, report back with ALL OF THE DETAILS asked for in the FINALLY section, the questions at the end of the troubleshooting link... most especially the codec used... see Question 1
Again... report back with ALL OF THE DETAILS asked for in the FINALLY section, especially Question 1
Out of sync problems are most often related to your source video.
What type of camcorder is your video coming from? Have you ensured that you're using the right project preset for that type of video?
You can find information on setting up project presets in my books, available on Amazon, and in my free tutorials Basic Training with Premiere Elements on Muvipix.com.
Welcome to the forum.
Take Steve's and John T's questions to heart. The answer probably lies within those answers.
If not, then this ARTICLE might be useful.
Also, and heavily dependent on the source material, editing an AV file is vastly different from just playing an AV file. Having good playback in a simple player program is not THAT relevant to how that same file will edit - very, very different operations.
Please let us know all about your source footage (your AV file), and look carefully at the questions posed by others.
PS - I would like to think that you will get much better "support" here, than from Adobe T/S. Here's hoping!