When ArcGIS applications fail, or are behaving strangely, one of the first things to try is to reset your application template document (ArcMap's is "Normal.mxt") or the entire ArcGIS application profile. This resolves many problems with ArcGIS software.
It's a good idea (with ArcMap) to do this every few months, or whenever a service pack or update is applied to ArcGIS, as these template files can gradually fill with cruft and slow down your ArcGIS Desktop applications. Application profile resets are rarely needed with ArcGIS Pro.
These steps do not require elevated privileges / admin access, as all users own their personal %APPDATA% folder.
