When I export my recordings from Audacity they now become "silent". Why? It always worked fine until recently

I have Audacity 3.5.1. It’s always worked perfectly till recently. My current problem = I record my acoustic guitar playing on Audacity, and everything works fine “until” I export the Audacity recording to my computer. When I play the recording all I hear is silence. My recordings are just mono, with 1 microphone, that’s it. I export them from Audacity as mp3 files. I’ve tried other formats like WAV etc but they also are silent. I can hear the music on Audacity. Any suggestions?