Yesterday I was on my computer and I upgraded my RealPlayer. I don't know if this is what caused it, but all of my music files(even though they were and still play in Windows media player by default) had the suffix .mp3 added to their filename. Now, when I change the name of a file, it changes the file type from mp3 to unknown. Why is this happening? Anyone follow what I'm saying?

Does the same thing happen if you change the file name at it's actual location on your computer?

Yes, that is where I am changing the name at.

Sounds to me like you have disabled "hide extensions for known file types" setting in folder options. This means that you can now see the .mp3 suffix on all your filenames. When you rename any files, if you don't put that .mp3 filename back on they will not be identified as music files (although from within media player they will probably still work)

To solve this problem either re enable the "hide extensions for known file types" setting:

Open "My computer"
Click the "tools" menu & choose "Folder Options"
Click the "View" tab and put a tick back in the "hide extensions for known file types" check box.

Or you can simply start putting .mp3 at the end of all your music filenames. I would suggest the former option:)

That's exactly what was going on. Thanks so much... it was really driving me insane. No more .mp3 on all my files.