Having a password or not is really useless. That can simply be fixed by formatting windows, so if the person has any basic knowledge of a computer, you're likely going to have to prove another way it's yours.
On a side note, whenever I have roommates, the day they move out, I rekey my locks. Of course I have trust issues. I had my dad staying with me for two months due to my parents splitting up, and when he moved out yesterday, the front and rear door locks were rekeyed, and that's my father. lol