Just a note, when turning on borders everywhere like this, it isn't necessary to actually "select" them, and you only need to turn on one parameter, the others will get turned on by default.
Dim LR as Long, LC as Long

LR = Range("A" & Rows.Count).End(xlUp).Row
LC = Cells(1, Columns.Count).End(xlToLeft).Column

Range("A4", Cells(LR, LC)).Borders.Weight = xlThin