This is Indexing problem.
Type Indexing Options. Get Indexing running. If not, Run in services.msc>Windows Search, if can't, be sure to start with Administrator's privilege, if not, use command "runas /user:<computername>\administrator cmd"
If still can't start Windows Search in services, then be sure to set zero (0) to HKLM\SOFTWARE\Microsoft\Windows Search>SetupCompletedSuccessfully
The above worked for me. But other alternative suggestions I didn't try are: 1. Go to Windows Features (turn on and off) and check Search Indexes, or 2. Go to Install/Uninstall Programs>Microsoft Office 365>Change>Repair.