XP - Desktop and licences lost - double tree in Documents and Settings

after normal reboot, the XP system came up with empty
desktop. Shows only standard default XP icons. All settings
referening
Outlook Express Documents and product licences lost, including
Norton antivirus licence. Looking at structure at Document
and Settings, there are now two tree:
c:\Documents and setttings\user_name
c:\Documents and setttings\user_name.host_name

What happned .. setup? .. XP fault? .. virus? How to return
to originial settings without loosing data, settings and
procuct licence ?

thanks in advance for your hints