Trouble Importing Audio files to record on Cakewalk.

I bought the Samson co1u microphone with Cakewalk software a few weeks ago. I've basically figured everything out except for importing files. I use the software on both computers in the house, one is Windows XP, and the other is Windows Vista, both respond the same.
When I choose to open a current file, I can import the files that come with the mixer, such as tutorials and demos. But when I choose to just import my own music and mp3s to record with, I always get a message that says the file is either un readable or a file that doesn't work through cakewalk. I have downloaded several file converters and tried to import over and over but it always says the same thing.
It says it needs to read an mp3 but all the music I have is ALREADY in mp3 form. I have gone through all my music folders and none of the tracks work or will uplaod.
 
A second thing it also does, when I try to import or open tracks from the computer or from cds, the songs simply DO NOT show up. I can find the folders, click on them and open them, but when they are opened they are empty. For example.
I see a file I have called "Christmas music", I know for a fact it should have 12 songs in it, so when I click on it, there is nothing in the folder.
Would love if I could get step by step help.