Make cell entry in a range mandatory

I have a sheet that lists names, towns and whether a person has been checked.

What I would like to do is when I enter something into cells A2 to A1000 then cells B2 to B1000 and E2 to E1000 become mandatory to have to enter something into.

Could someone help me with this please.

Thank you.

Thank you 6StringJazzer. That's the kind of solution I'm after however when I enter something into column E and go to select a cell in column A to enter the next name, Excel hangs (not responding). Any ideas why this might be please?

Originally Posted by h4a4r6r6

Thank you 6StringJazzer. That's the kind of solution I'm after however when I enter something into column E and go to select a cell in column A to enter the next name, Excel hangs (not responding). Any ideas why this might be please?

You may find JeteMc's solution a better fit, as it does not require macros. However, here is a fix for the problem in mine. I neglected to turn off events so that when the code makes a selection, it calls itself infinitely.

Private Sub Worksheet_SelectionChange(ByVal Target As Range)

   Dim R As Long
   
   Application.EnableEvents = False
   
   If Cells(Target.Row, "A") <> "" And Target = "" And (Target.Column = 2 Or Target.Column = 5) Then
      ' user is about to fill in a required field, do nothing
   Else
      R = 2 ' first data row
      Do Until Cells(R, "A") = ""
         If Cells(R, "B") = "" Then
            MsgBox "You must provide " & Cells(1, "B") & " for " & Cells(R, "A") & " before continuing"
            Cells(R, "B").Select
            Exit Sub
         ElseIf Cells(R, "E") = "" Then
            MsgBox "You must provide " & Cells(1, "E") & " for " & Cells(R, "A") & " before continuing"
            Cells(R, "E").Select
            Exit Sub
         End If
      Loop
   End If
   
   Application.EnableEvents = True
   
End Sub