Hey, I am on my administrator PC, the main account. My sister added a password to it, and didn't turn the PC off, I don't know the password, so how do I remove it?
Nope, either your sister tells ya, or get ahold of the manufacturer and prove ownership and they may be able to help. Even asking to bypass a PW is against forum rules.
We cannot help as you have no way of proving to us that you have any right to be accessing the computer.
OR to put it another way. If you had set a password on your computer because you had private things on it and your "sister" had came here asking for help to access it, and we had helped her, how would you feel about it then?