problem in tables relationships

hi all,

i intend to design a institute management database.therefore i have 4 tables

1)institutes table (contains the names of all of institutes )

ID autonumber , Institute_Name

2)courses table (contains all of the courses existed in every institute)

ID autonumber , Course_name , INS_ID "to connect to institutes table"

3)students table (contains the names of students in each course in institute

ID autonumber, Student_name, CRS_ID "to connect to courses table"

4)subjects table (contains the subjects included in every course)

ID autonumber, Subject_name, CRS_ID " to connect to course table "

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provided that every student can not be registered in more than one course and can not be in more than one institute each time.

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the problem is that , when making a subform i can not enter nor update data also ms access made student name and subject name fields in same table but in real they are two different tables.

please help

problem in tables relationships