Have a look at the Sticky thread & its links at the top of this section. ALso make sure you have a player that can play all types of audio or else, make sure you have all audio codecs necessary for the file. eg: For m4a using WMP you will need the 3ivx codec. Also make sure you have the latest wmp codecs.
Else get a better player such as QCD:
http://www.quinnware.com/ or some other decent players: 1.
dBpowerAMP,
- 2.
WinAmp, - 3.
Quintessential (QCD), - 4.
iTunes
* Good tagging tools:
http://massid3lib.sourceforge.net/