User profile

Set up new laptop with Vista Home Premium a few weeks ago. Installed
software, configured desktop and started using.
Suddenly, when booting up, I get error message "Your user profile was not
loaded correctly. You have been looged on with a temporary profile".
Simultaneously, my desktop returned to basic configuration, my startup files
no longer included my preferences etc.
Any suggestions how I can get the user profile loaded again?

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Roger