check cells

This looks to work.

Option Explicit

Sub Test()

Dim i As Integer, j As Integer
Dim cell As Variant
Dim rng As Range

Set rng = Worksheets("Before").Range("C4:F11")
 For i = 4 To 11
  For j = 3 To 6
   For Each cell In rng
    If Cells(i, j) = "" Then
     MsgBox ("Please fill all Cells in the above range")
  Exit Sub
    End If
 Next
  Next
   Next
   
End Sub