Hey. Im the administrator on my pc, so is it possible to make another pword somewhere if...(cont below!)?

Someone else bypes my start-up screen pword (pressing f8 and going onto the safe mode etc...) Can i use another pword so the other person CANNOT get into my files? Thanx in advance. By the way, im asking this because i split with my gf earlier and i dont want her getting into my pc and deleting all of my important work doents.