dood the problem u stated clearly seems to be the files itself

if ur system dosent have a codec which is required to play a certain file then the file wont get opened in the first place

as for kazaa ..... not everything u download on kazaa works

many time during download the files get corrupt and thus r rendered useless

so nuthin wrong with ur system

neway if u dont have it do load windows media player v9 + updates

enjoy