If you are using the Check Box as a toggle then you need to add that to the Record Source so it knows which ones to not show. What is the Record Source of your Subform?
As for linking no not Relationships, you need to link the forms...
Link Master Fields
Link Child Fields
So that the Parts showing in the SUbform are the Oarts that go with that Company.
Now, when you say the Relationshios aren't working, what exactly does that mean? If you have not established Relationships because it won't let you then there is another problem that needs to be dealt with ASAP. Can you upload your database? We need to see what is causing that... (Note: You can empty it, we don't need the data.)