Lost all information

We recently got this dell computer with windows vista. Somehow it has lost
all information. All of my email addresses, my background and pictures all of
my saved favorites in explorer. It even deleted my email and my husband had
to add it back. It came up with an unexpected error or windows shutdown
occured (it has happend several times, but never deleted anything. It cant
find a fix? I did go into the "my computer" section and I can view the recent
emails and recent documents, but I dont know how to get it back. It has a
trend Micro PC thing that comes up to check for viruses? any suggestions?
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mlb