Sorting A Very Hidden Sheet That Is Not Active

I have tried to use absolute references (perhaps I didn't do it right) but it didn't work. Below is the code that does work but I need to first make the sheet visible then activate it.
Sub Row_Sort(tmpsheet As String)
' Sort the first 4 columns of the tmpsheet sheet

Dim tmprng As Range
Dim OldActiveSheet As Worksheet

' Activate the desired workbook (in this case Linewkbk)
Workbooks(LineWkbk.Name).Activate

' Save old active sheet
Set OldActiveSheet = ActiveSheet.............