Select the cells where input is required and set their format (Protection tab) to unlocked. Now protect the worksheet (review ribbon) and only those cells will be editable.
Try this in the Thisworkbook code-module (you will probably change what sheet it refers to):
Code:
Private Sub Workbook_Open()
With Sheets("Sheet1")
.Protect userinterfaceonly:=True
.Cells.Locked = True
.Range("C3, C4,C7:E7, C9,C11,C13,C15:E17").Locked = False
.EnableSelection = xlUnlockedCells
End With
End Sub