When using SUM() it automatically combines all rows into one.
The solution is to use a nested SELECT statement. I think it is more efficient to do that in the form of a cross join like:
SELECT sumtable.afrTotal, orderdetails.DetailID, orderdetails.DetailSchool, orderdetails.DetailStudentF, orderdetails.DetailStudentL, orderdetails.DetailPrice FROM orderdetails CROSS JOIN (SELECT SUM(DetailPrice) AS frTotal FROM orderdetails ) AS sumtable ORDER BY DetailStudentL ASC