Using vba to index - match to a different worksheet

Hello,
The following code is something I've been trying to get to work for a couple of hours now.
I'm not that great at VBA scripting as I've just been teaching myself over the last couple of weeks.
Any help with this would be apreciated.

The problem is that the code I've made to extract the value for "BATCH / SERIAL" that corrosponds to the "PO" from another spreadsheet (which uses =indirect() forumlae so I have to open another spreadsheet too) doesn't work It just doesn't find the value even though it's in there.

SETUP:
Worksheets("CONC DESCRIPTION").Select
Cells.Select
Selection.ClearContents

DIMENSION_VARIABLES:
Dim INPUT_VAR As Variant
Dim RESPONSE As Variant

SET_PO:
INPUT_VAR = 0
INPUT_VAR = Application.InputBox("INSERT PO", "PO")
If INPUT_VAR = False Then
    GoTo EXIT_SUB
    Else
    If INPUT_VAR = "" Then
        MsgBox ("IS NOTHING")
        GoTo SET_PO
        Else
        If Len(INPUT_VAR) = 9 Then
            If IsNumeric(INPUT_VAR) And Val(INPUT_VAR) > 0 Then
                Else
                MsgBox ("NONNUMERIAL OR NOT >0")
                GoTo SET_PO
            End If
            Else
            MsgBox ("LEN =/= 9")
            GoTo SET_PO
        End If
    End If
End If

ADD_PO:
RESPONSE = MsgBox("PO: " & INPUT_VAR & " - CORRECT?", vbYesNo)
If RESPONSE = vbNo Then
    MsgBox ("TRY AGAIN.")
    GoTo SET_PO
    Else
    Application.Cells(12, 1) = "PO"
    Application.Cells(12, 2) = INPUT_VAR
End If

SET_SERIAL_OR_BATCH:
Application.Cells(13, 1) = "SERIAL/BATCH"
Dim SERIALVPO As Workbook
Dim SPARTRACK As Workbook
Set SPARTRACK = Workbooks.Open("X:\A350XWB Manufacturing\General\5020 Concessions\Concession Status\Copy of A350 Rear Spar Serial Number log.xls", True, True)
Set SERIALVPO = Workbooks.Open("X:\A350XWB Manufacturing\General\5020 Concessions\Concession Status\SERIAL V PO.xls", True, True)
RESPONSE = Application.Match(INPUT_VAR, SERIALVPO.Worksheets("SERIAL V PO").Range("E1").EntireColumn, False)
If (Not RESPONSE Is Nothing) Then
    Application.Cells(12, 2) = SERIALVPO.Worksheets("SERIAL V PO").Range("D" & RESPONSE).Value
    Else
    MsgBox ("SERIAL / BATCH NOT FOUND")
    SERIALVPO.Close False
    SPARTRACK.Close False
    Set SERIALVPO = Nothing
    Set SPARTRACK = Nothing
    GoTo SET_PO
   End If
SERIALVPO.Close False
SPARTRACK.Close False
Set SERIALVPO = Nothing
Set SPARTRACK = Nothing

Cheers.

Hutchay

also I'm also struggling with the following:

PUT_IN_WORD:

OPEN_WORD:
Dim wordapp As Object
Set wordapp = CreateObject("Word.Application")
wordapp.Visible = True
wordapp.Documents.Open "X:\A350XWB Manufacturing\General\5020 Concessions\TEMPLATES\BLANK.doc"

COPY_AND_PASTE_INTO_WORD:
Range("A1:A10").Copy 'FIRST LINE AND DIV 1
'PASTE UNFORMATTED TEXT
INPUT_VAR = Application.Cells(23, 2)
DIV = 2
Do While INPUT_VAR > 1
    Range(Cells(3, DIV), Cells(10, DIV)).Copy
    'Paste UNFORMATTED TEXT
    DIV = DIV + 1
    INPUT_VAR = INPUT_VAR - 1
Loop
Range("A11:A13").Copy 'LAST 3 LINES
'PASTE UNFORMATTED TEXT
Range("A14:B25").Copy 'INFO TABLE
'PASTE WITH FORMATTING
'wordapp.Selection.PasteSpecial DataType:=wdPasteText
'Application.CutCopyMode = False

SAVE_WORD:
wordapp.document.Save
'SAVE as - in specific location

It's part of the same macro.. not sure why it doesn't work

To set "RESPONSE" as the row number in which "INPUT_VAR" is found in the column E:E of the spreadsheet "SERIAL V PO.XLS".