This should find the last file for the month corresponding to the cell in column B
[vba]
'Select the worksheet to get data from
Dat = ThisWorkbook.Path & "\report " & _
Format(Month(DateValue(ActiveCell.Offset(, -1))), "00") & "-"
For i = 31 To 1 Step -1
testname = Dat & Format(i, "00") & ".xls"
If Len(Dir(testname)) > 0 Then
Workbooks.Open(Filename:=testname).RunAutoMacros Which:=xlAutoOpen
Sheets("PC").Select
ActiveCell.SpecialCells(xlLastCell).Select
Exit For
End If
Next
[/vba]