LINQ to OBJECT(HashTable)

Scenario:

A detail class(Marks), which contains Object of a Structure(MarkDetails) as Data Member. There are some member functions like AddorUpdateRecord which is use to update data.
Another class named "MarksInfo" containing HashTable. The HashTable contains the object of class "Marks" as value fields and some key, (Hashtable will have one entry per student).

Requirement: We need to make DataTable that contains marks of all the students.