Greetings.
it did not read .dat originally, just an unassociated file type, i right clicked to discover that it was a .dat!
I'm not sure if you have done this or not, but base on what you have mentioned above, I guess not.
1) Go to the folder which contains your "mp3" file.
2) Go to Tools -> Folder Options.
3) Select the tab "View".
4) Uncheck this: "Hide file extensions for known file types".
5) Click "OK" and now I guess you can see your_song.dat right?
Or according to the previous post, you have changed the extension
to .mp3, so I guess the file would now be: your_song.mp3.dat.
6) Now, change it to your_song.mp3.
After that, you could go back to Tools -> Folder Options, & have the "Hide
file extensions for known file types" be checked once again (your wish.).
Did that help?
Thanks.