you don't mean the whole page, do you?  You probably mean the whole group of sections if the details have a negative value.  If the second, because the first will return a blank report, I would create a subreport to search the detail records in question.  I would then set a shared variable to report back if the group has a negative value.  Then I would go into Section Expert and suppress all the sections if the shared variable indicates a negative value.  The same would be true for the first option, but the problem with Crystal is that you don't 'know' where a page is.

section expert: suppress button.