Hi Dennis,
I'm in the same boat as you. Yesterday I was having a perfectly normal day, finishing off some edits to a course, and when I went to go Publish it was slow, then stalled, and eventually froze. I then realized that I lost the ability to even preview the project, a scene, or a slide.
I know other people who started having the same issue at the same time. I was worried the course itself had become corrupted, but I had the same issue with a new/blank project AND I was able to send the file to someone else and they had zero issue publishing and previewing the course.
I'm commenting in hopes an admin or staff will see it and escalate this issue, because being unable to Preview/Publish is is a major issue. Did you recently do an update to Storyline, or do you have a pending update when you go to open? Is there anything else you've observed?
If I find out anything, I'll be sure to let you know!