Raw import won’t work with a compress file. Compression is a lot like encryption and you’ll get noise-garbage if it’s not decoded properly.
Go to Edit → Preferences → Modules and make sure mod-mp3 (and everything else) is enabled.
If that’s not the problem, the MP3 is corrupt of invalid, or it’s not really an MP3. But no matter what the problem, if another application can play it a different file conversion program may be able to convert it to WAV, which you can then open in Audacity.