Try this:
Sub highlight()

'

' highlight Macro

    Workbooks.Open Filename:="S:\Reports\78weeks.xls"

    With Columns("I:CH")

        .FormatConditions.Add Type:=xlCellValue, Operator:=xlLess, Formula1:="=0"
        .FormatConditions(.FormatConditions.Count).SetFirstPriority

        With .FormatConditions(1)
            With .Font
                .Color = 393372
                .TintAndShade = 0
            End With

            With .Interior
                .PatternColorIndex = xlAutomatic
                .Color = 13551615
                .TintAndShade = 0
            End With

            .StopIfTrue = False

        End With

    End With

    Range("A1:A2").Select

    ActiveWorkbook.Save

    ActiveWindow.Close

End Sub