How to SELECT by MAX(date)?

This should do it:

SELECT report_id, computer_id, date_entered
FROM reports AS a
WHERE date_entered = (
    SELECT MAX(date_entered)
    FROM reports AS b
    WHERE a.report_id = b.report_id
      AND a.computer_id = b.computer_id
)

Are you only wanting it to show the last date_entered, or to order by starting with the last_date entered?

SELECT report_id, computer_id, date_entered
FROM reports
GROUP BY computer_id
ORDER BY date_entered DESC
-- LIMIT 1 -- uncomment to only show the last date.

Accordig to this: https://bugs.mysql.com/bug.php?id=54784 casting as char should do the trick:

SELECT report_id, computer_id, MAX(CAST(date_entered AS CHAR))
FROM reports
GROUP BY report_id, computer_id