Excel VBA - index and match vba error

I haven't gone through all the code checking for issues, but the main ones were:

1. You weren't properly qualifying your Range and Cells calls with a worksheet object;
2. You can't use Range(cells(x, y)) unless the value of the cell at Cells(x, y) is the address of a range.
3. Your parentheses weren't correct in the Index / Match part.

Try this one:

Sub MergeAllWorkbooks2()

    Dim FolderPath            As String
    Dim X                     As Long
    Dim i                     As Long
    Dim FileName              As String
    Dim WorkBk                As Workbook
    Dim SourceRange           As Range
    Dim DestRange             As Range
    Dim wsDest                As Worksheet


    'path of directory
    FolderPath = "C:\Users\XXXX\Desktop\New folder\XXXXX\"

    ' Setting starting points
    X = 3

    ' Call Dir the first time, pointing it to all Excel files in the folder path.
    FileName = Dir(FolderPath & "*.xl*")

    ' Loop until Dir returns an empty string.
    Do Until FileName = ""
        ' Open a workbook in the folder
        Set WorkBk = Workbooks.Open(FolderPath & FileName)

        'Set the source range
        Set SourceRange = WorkBk.Worksheets(1).Range("C2:C7")

        ' Set the destination range
        Set wsDest = Workbooks("Summary.xlsm").Worksheets("Sheet1")

        Set DestRange = wsDest.Range(wsDest.Cells(4, X), wsDest.Cells(9, X))

        ' Copy over the values from the source to the destination.
        DestRange.Value = SourceRange.Value

        'Get hourly from each file
        For i = 12 To 8762
            wsDest.Range(wsDest.Cells(12, X), wsDest.Cells(12, X).End(xlDown)) = _
            Application.WorksheetFunction.Index(WorkBk.Worksheets(2).Range("B3:B8762"), Application.Match(wsDest.Cells(i, X), WorkBk.Worksheets(2).Range("A3:A8763"), 0), 1)
        Next i

        ' Increase NColumn so that we know where to copy data next.
        X = X + DestRange.Columns.Count

        ' Close the source workbook without saving changes.
        WorkBk.Close savechanges:=False

        ' Use Dir to get the next file name.
        FileName = Dir()
    Loop

    '    Range("C4:C9", Range("C4:C9").End(xlToRight)).Sort key1:=Range("b7"), key2:=Range("b8"), key3:=Range("b9"), _
         '     order1:=xlAscending, Orientation:=xlLeftToRight

    endTime = Now()
    totTimeSec = Round(((endTime - startTime) * (24 * CLng(3600))), 1)
    MsgBox (totTimeSec & " seconds")

End Sub