well for one windows media player is crap and cant play half the mp3's I throw at it. I like winamp personally. I hear the gom player is good to, not quite sure what that quick player is and itunes yah dont get me started >_>. Anyways try those 2 players and see if that helps. I did notice that on some of them they just didnt work and winamp can play dang near everything u throw at it well audio anyways for vid files needs a codec but anyways try that, but yah if they didnt work with my winamp I just removed them and was like eh I got way more than I lost anyways. Let me know if that helps. Usually the reason they wont work or w/e is they werent uploaded right or they weren't encoded right.