VBA - Search files in a folder, copy IF problem

[JooMa]

Hi everyone!
I'm a total VBA newb and I require some professional assistance getting my code to work.
I've searched far and wide with no luck and I'm getting quite desperate.
All kind of help will be greatly appreciated!

In short, I need my code to search through Excel workbooks in a predestined folder and copy rows to my master workbook (where the macro is) if three spesific conditions are being met (start & end date and product number).
This is how far I've gotten modifying different bits and pieces to suit my needs:

Sub Etsiva_click()

'Macro optimization
    With Application
        .ScreenUpdating = False
        .EnableEvents = False
        .Calculation = xlCalculationManual
    End With

'Sourcefolder and filenames
    Dim FolderPath As String, FileName As String
    FolderPath = "C:\Users\MYUSERNAME\Documents\Projects\Excel\Tests\Data\"
    FileName = Dir(FolderPath & "*.xl*")
    
'Workbooks and sheets
    Dim WorkBk As Workbook
    Dim WorkSht As Worksheet
    Dim TemPest As Worksheet
    Dim ActIon As Worksheet

'Search definitions
    Dim nRows As Long, LastRow As Long
    Dim CurYear As Date, StartDate As Date, EndDate As Date
    Dim ProDuct As String
    
'Count last used row and define starting row
    LastRow = Cells(Rows.Count, 1).End(xlUp).Row And Cells(Rows.Count, 4).End(xlUp).Row
    nRows = 3
    
'More workbooks and sheets
    Set TemPest = ThisWorkbook.Worksheets("Temp")
    Set ActIon = ThisWorkbook.Worksheets("Actions")
    
'Search criteria
    StartDate = ActIon.Range("A2").Value
    EndDate = ActIon.Range("A3").Value
    ProDuct = ActIon.Range("A4").Value
    
'Empty "Reporting" (this workbook) "Temp" -sheet before copying new data
    TemPest.Range("2:7").ClearContents

'Loop and copy
        Do While FileName <> ""
            If FileName <> ThisWorkbook.Name Then
                Set WorkBk = Workbooks.Open(FolderPath & FileName)
                WorkBk.Activate
                Set WorkSht = WorkBk.Worksheets("Sheet1")
                With WorkBk.Worksheets(1)
                    Do
                        If WorkSht.Cells(nRows, 4).Value <= EndDate And WorkSht.Cells(nRows, 4).Value >= StartDate And WorkSht.Cells(nRows, 1).Value = ProDuct Then '***
                            TemPest.Cells(nRows, 1).Value = WorkBk.Worksheets("Sheet1").Cells(nRows, 1).Value   'Product number
                            TemPest.Cells(nRows, 2).Value = WorkBk.Worksheets("Sheet1").Cells(nRows, 2).Value   'Product
                            TemPest.Cells(nRows, 3).Value = WorkBk.Worksheets("Sheet1").Cells(nRows, 3).Value   'Variable
                            TemPest.Cells(nRows, 4).Value = WorkBk.Worksheets("Sheet1").Cells(nRows, 4).Value   'Date
                            TemPest.Cells(nRows, 5).Value = WorkBk.Worksheets("Sheet1").Cells(nRows, 5).Value   'Time
                            TemPest.Columns("A:A").SpecialCells(xlCellTypeBlanks).EntireRow.Delete              'Delete empty rows
                        End If
                    nRows = nRows + 1
                    Loop Until nRows = LastRow + 1
                    WorkBk.Close SaveChanges:=False
                End With
                FileName = Dir
            End If
        Loop

'Macro optimization off
    With Application
        .ScreenUpdating = True
        .EnableEvents = True
        .Calculation = xlCalculationAutomatic
    End With

End Sub

***This row is giving me '1004' Application defined or object defined error and I'm not sure why. There might be some other anomalies in my code too, but I haven't made that far yet.