During installation you should be prompted to create your own administrative account so that "Administrator" can be reserved in case of emergency. However, if you don't create one you will automatically be logged in as Administrator. I don't know why you are losing access to your files, however.
I'm running Windows XP H.E. SP2 on my home computer. I'm the only user, owner, etc. When I install Windows and am the only user, do I automatically become "The Administrator"? After years of computing, for some reason I'm recently losing ownership of various files... getting and "access denied" warning. Usually I can go into security and give myself ownership. I don't know what I'm doing to lose possession of the files. Does anyone have any ideas?