There's a known issue where quitting Premiere while in Import or Export mode will cause those modes to be blank after relaunch. The workaround is to switch back to Edit mode, quit Premiere and relaunch. Import & Export modes should be functional again after that.
I have the same issue. All I see is the loading icon. It won't let me export the video in any way. The only way it shows is if there's no clips on the timeline, as soon as I add any clip it goes back to a loading mode.