CODECs list for Movies/Audio/ Alternate players & check the codecs list. There are some specifically for windows users. There's also others such as freecodecs where you can search mp3 codecs.

Sounds like either your mp3 codec is oldish or the file(s) are mp3pro which you do not have a codec for.
* Remember to be aware of fake mp3's:
Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see) & remember those file sizes.