Well with what little info your giving its hard to understand whats going on. If you were my kid and you suspected either me, "mom", or your brother is messing with the computer your best bet would be to ask your folks if they had. If they have been say ok and its all done, if not you might ask them to ask your brother if he's been messing with it and why?
Here in my house all of this would be ok and if it wasn't one of us parent type I'd have my other son hanging over the hot coals to find out what hes up to. On the other hand if I found a keylogger, or was locked out of one of my sons computers the solution would be easy. I'd unplug it, bring it out back, and cut it in half with a chainsaw, and then return it to his room. He would then buy his own computer AFTER he got his own apartment.
Just because a computer is in your room, our you bought it with your own money, doesn't make it yours if you still live at home. Now if your away at college and your worried about a room mate, or others roaming through your room I'd say you have a case.