Exporting to mp3

I downloaded Audacity then recording from my cassette on to the computer, Everything seems to playing back fine, I downloaded LAME for the .dll, then I allowed audacity to find the .dll. But when I go to export as an mp3, it says it does it, but when I go to listen to that mp3, there is no audio, just a file with no sound that is the same length as the recording I took. I’m confused on why the audio isn’t coming through after I export. Please help

Import the MP3 back into Audacity. Does it have the same blue waves as the recording? If so, and this is a USB cassette player, see this Frequently Asked Question:
http://manual.audacityteam.org/o/man/faq_playback.html#usb .