adding new files to directory

I add a new file to my music directory, over 750 files but the new files are not showing up in Mp3Tag.
The files are there. I can access them and play them in Windows 7. Cannot edit the tags however.

What kind of files are they? Do they have tags?
WAV files do not have tags.
MP3tag does not update the list if you add files with a running MP3tag. You have to refresh the list e.g. with F5.
Did you set a filter that hinders MP3tag to show the files?

They can have but are not supported by Mp3tag.