Hello @cathym4023 ,
You might be running into a connectivity error, since your email previews are coming up for me both in-editor and on the My Campaigns screen. Let’s start with some basic connectivity troubleshooting. Please keep in mind that when I say connectivity issues, I'm not necessarily referring to just your internet speed.
If none of those alleviate the issues, could you please provide a screenshot of your speed test, including the More Info section? Once we have that we can do some more advanced troubleshooting as needed.