Option Explicit

Private Sub Application_Startup()
Dim xlApp As Object
Dim xlWb As Object
Const strWorkbook = "C:\Path\WorkbookName.xlsx"
    On Error Resume Next
    Set xlApp = GetObject(, "Excel.Application")
    If Err <> 0 Then
        Set xlApp = CreateObject("Excel.Application")
    End If
    On Error GoTo err_Handler
    xlApp.Visible = True
    'Open the workbook to input the data
    If FileExists(strWorkbook) Then
        Set xlWb = xlApp.workbooks.Open(strWorkbook)
    Else
        MsgBox "Workbook is missing!"
        GoTo lbl_Exit
    End If
    'do seomething with the workbook here
lbl_Exit:
    Set xlApp = Nothing
    Set xlWb = Nothing
    Exit Sub
err_Handler:
    Err.Clear
    GoTo lbl_Exit
End Sub

Private Function FileExists(filespec) As Boolean
Dim oFSO As Object
    Set oFSO = CreateObject("Scripting.FileSystemObject")
    If oFSO.FileExists(filespec) Then
        FileExists = True
    Else
        FileExists = False
    End If
lbl_Exit:
    Set oFSO = Nothing
    Exit Function
End Function