Are you in the 'administrators' system group then?
What it sounds like is all your files are actually 'owned' by the administrator group rather that you. You'd need change the ownership of all your stuff (you can do that at the top of the folder tree and it should flow down) and then take yourself out of the admins group. Then you'd have access to your stuff but nothing else. Of course that means you'll no longer be able to administer things and won't be able to put yourself back in the group either, so make sure someone else is in the group before you do that
