Stan,
Right click on your sheet tab, left click on View Code, and paste this in:
Private Sub Worksheet_Change(ByVal Target As Range)
Select Case Target.Address
Case "$A$1"
ActiveSheet.Unprotect ("PASSWORD")
Range("$B$1:$D$1").Locked = True
ActiveSheet.Protect ("PASSWORD")
Case "$B$1"
ActiveSheet.Unprotect ("PASSWORD")
Range("$A$1:$D$1").Locked = True
Range("$B$1").Locked = False
ActiveSheet.Protect ("PASSWORD")
Case "$C$1"
ActiveSheet.Unprotect ("PASSWORD")
Range("$A$1:$D$1").Locked = True
Range("$C$1").Locked = False
ActiveSheet.Protect ("PASSWORD")
Case "$D$1"
ActiveSheet.Unprotect ("PASSWORD")
Range("$A$1:$C$1").Locked = True
ActiveSheet.Protect ("PASSWORD")
Case Else
Exit Sub
End Select
End Sub
It assumes the 4-cell range of interest is unlocked to begin with (that's logical), and that you've unlocked other cells on the worksheet already, having nothing to do with these 4 cells, that you will also want to enter data into without worrying about what happens with the 4 cell range.
Modify the cell addresses and password as needed.
Tom Urtis