Shared worksheet won't open Excel 2000

One of our user's can't open a couple of worksheets that
are located on a network drive. No error message is
displayed, just a plain old grey excel background with all
the toolbars, etc present and corect. She says no-one has
altered the permissions, which all seem to be OK - plus
she's the only one who can't open these particular sheets.
All other worksheets open fine and there's no other
problems with Office or her PC in general - any
suggestions??