Audacity 2.4.2. I have a bunch of mp3 files of things I have recorded that I need to edit. Audacity will not open the mp3 files? I have installed Lame. I downloaded ffmpeg. I downloaded avformat-55.dll. I put it in the Audacity program86 folder and in the document/audacity folder. I went to the preferences/libraries and located the avformat file. It still does not see it. What do I need to do to be able to edit my mp3 files?
Using RealPlayerConverter I converted my mp3 to wav. No problem doing that. Then I was able to open the wav file. I exported that one to mp3. Audacity opens the new mp3 file. So what would cause it to not be able to open the original mp3??? (This is on Windows 10)
Are you able to export from Audacity as MP3, and then import that MP3 back into Audacity?
Yes, it does import the mp3 exported from Audacity
Use this page to analyze the “MP3” files that don’t import: https://mediaarea.net/MediaInfoOnline
What does that page say about the files?
I have installed Lame. I downloaded ffmpeg. I downloaded avformat-55.dll. I put it in the Audacity program86 folder and in the document/audacity folder. I went to the preferences/libraries and located the avformat file.
Just FYI - None of that is used to open an MP3. 
LAME is used to export/create MP3s but it’s now built-into Audacity so you don’t have to install it. FFmpeg is used to import/export many other formats.
Sometimes you have a corrupt MP3 (or invalid or imperfect MP3) or you may have another format that’s just named “.MP3”. There was a recent change to Audacity and it no longer ignores MP3 errors so it’s more “picky” than it used to be and it’s more picky than some other programs.