Verify the following in order -

On the Reports page:

1. Ensure that "Only show my reports" at the bottom is NOT marked currently. If it is, unmark it.
2. Ensure that the tag "ALL" is marked to the left of the list of reports. If it's not marked, mark it, as that could be hiding some reports.
3. Test logging in with another user to see if it could be user specific
4. If the report still cannot be found, and does not show for any user, it may have been deleted. It's possible to create a new instance of the report.