Windows 10 Fall Creators Update includes a bug wherein you can’t rename files when File Explorer view mode is set to Small Icons. Nothing happens when you use the Rename button in the ribbon, or when you click Rename in the right-click menu.
This issue (“Files can’t be renamed when File Explorer is in Small Icon mode”) has been reported on the Feedback Hub, and upvoted by 40 users already. Microsoft might be aware of this issue and lets hope this gets fixed in the December Cumulative Update for Windows 10 v1709.
Until then, change the view mode to anything other than Small Icons, and rename the file. Alternately, right-click on the file, click Properties and change the file name in the General tab.