Hi Danielle!
Sorry to hear you're having trouble previewing and publishing a Storyline course!
Thanks for sharing the steps you've tried so far. To clarify, are you experiencing this issue across all .story files, or is the behavior local to one? I suggest performing a repair of your Storyline installation to see if that does the trick.
If still unsuccessful, it would be helpful to see a copy of the file that's giving you trouble. Feel free to share it here in the discussion or privately through a support case. We'll delete it from our system as soon as troubleshooting is complete!