What are the names of the files? NOT the names of the songs, the names of the FILES. if they're something like SONG123.MP3, that is the correct format. If they're anything else, like SONG123.CDA, you need a format converter. Many are free.

Specifically, we need to know the extension - the three (or sometimes four) lets after the "." in the filename, such as MP3, WMV, CDA or whatever.