Need help restoring system user/files

i updated my operating system the other night to 10.9.3, when i came up in the morning i had to set up my mac like i just got it with a new user, and I'm assuming it just gave me a new operating system user, and set the mac back its factory state and i can't seem to find the old one. iv gone thru looking at most of the options, can't seem to find the "deleted user" in users or any other place where the old user with all the files on it were. wondering what to to, if the files i lost are replaceable thanks. its my brothers laptop and he doesn't use timeline or anything to back up that i know of.