All of a sudden people started getting these errors while opening Excel files in the browser:
at C:\Windows\TEMP\Excel Server\FileCache\fa812204-b6ff-40ec-9209-fe8add3de89e\Ranges. Excel Services Application is unable to function without a workbook cache.
Thanks to below links, issue could be resolved
Unable to create or access workbook cache at C:\WINDOWS\TEMP\Excel Server\FileCache\SharedServices1-1078443246\Ranges. Excel Services is unable to function without a workbook cache.
(you can see this error in Event viewer)
Unknowingly you may have deleted the above mentioned folders. So, Excel services is not able to save the temporary files under the "Ranges" folder.
Login inside the SharePoint server and create the "Ranges" folder as per the above mentioned folder structure. If you are not able to see the "Excel Server" folder inside "C:\Windows\Temp" folder, just create it manually.