You don't need to select or activate a cell in order to work with it. The following loops through row A and colours the entire row if a 1 is found.
Dim LastRow As Long, i As Long
LastRow = Cells(Rows.Count, 1).End(xlUp).Row
For i = 1 To LastRow
If Range("A" & i).Value = 1 Then Rows(i).EntireRow.Interior.ColorIndex = 5