pst files not being seen

I had a user that was working in excel and a error message came up indicating the outlook pst files could not be viewed. I searched the harddrive and no pst files. They were not deleted. Has anyone heard of this? what was their solution if heard.The user has a dell optiplex gx110 with windows 2000, with office 2000. Thanks for any help that can be given.

Markus