There are several issues here. First its not good practice to create a form based on multiple tables. Too often such forms may not display data. And that is probably the issue here. The form probably has not data in its recordsource.
So first, I recommend that you use a mainform/subform combination. The Mainform should be bound to the Participant table and then you should have subforms for the other two tables.
You should build your form piece by piece. First the mainform and make sure it works. Then build the subform as a separate form, make sure they work. Then embed each subform on the main form, in turn. Check that each works.
See if that helps, if not post back with any error messages and we can try other solutions.