Excel sheet Hidden Rows from 1 to 4080

If you [CTL] + A several times you should select your entire workbook, then right click on mouse and select unhide.

If you can get to the VBA editor, you could do something more surgical like 

Sub unhideTopRows()
    Dim ws As Worksheet
    Set ws = ActiveSheet
    Range(ws.Rows(1), ws.Rows(4000)).EntireRow.Hidden = False
End Sub