Lost configuration, documents, desktop folders and files

Hi there, I am trying to fix a friend's computer with vista ultimate. Her
computer had rebooted to a fresh user with no documents or programs installed
with the same name she had before. I was able to find the files and copied
and moved them to the documents folder or desktop again.
It seemed to work, but today everything got lost again from the desktop. I
ran a NOD32 virus deep scan, nothing came out. I am doing windows update, it
looked as if she had no updates (a >450 Mb download), and this time the
desktop folders and files I had found seem to be lost for good. What is going
on here?
Dell inspiron 4000, 1 gb RAM, centrino duo 1.73 ghz, ati mobility radeon
x1400, 32 bit windows version.