Lets use something that is not ours shall we?

Yesterday I came home and discouvered that my sister was on my computer and my mom freaking defended her saying that it was okay. I asked my dad and he say that it was not okay. I brought the computer not you and there for you have no right and u need to asked and wait for my answer! I waited 20 years to have my own computer and i don't want u using it and break it!