Hello @GayleM855 ,
Some browsers or slower internet speeds may cause the thumbnails to not display unless explicitly promoted to. Are you receiving an error message when you click on the Show Image icon, or when clicking the eye symbol and Preview icon on the email's reporting page?
Does performing any basic connectivity troubleshooting alleviate the issue at all? Please keep in mind that when I say connectivity issues, I'm not necessarily referring to just your internet speed. There are a number of elements that can affect website connectivity and accessibility on an individual basis.