Prevent macros running after message box show

I just got a code from stnkynts

Sub RunMe()
Dim icell As Integer

For icell = 1 To 4
    If Range("A" & icell).Value = "" And Range("B" & icell).Value <> "" Then
        MsgBox ("There is an error in Row " & icell)
    ElseIf Range("B" & icell).Value = "" And Range("A" & icell).Value <> "" Then
        MsgBox ("There is an error in Row " & icell)
    End If
Next icell

End Sub

And when I combine with my other code like:

Sub RunMe()
Dim icell As Integer

For icell = 1 To 4
    If Range("A" & icell).Value = "" And Range("B" & icell).Value <> "" Then
        MsgBox ("There is an error in Row " & icell)
    ElseIf Range("B" & icell).Value = "" And Range("A" & icell).Value <> "" Then
        MsgBox ("There is an error in Row " & icell)
    End If
Next icell

Range("A1:B1").Value = vbNullString
End Sub

Every time message box appears and click OK ... the value in the cell erased
if the many data is entered it will be hard to type it again
Is there any code to prevent the value in the cell is not deleted before editing

Thanks in advance