Moodle self-enrolment has two switches: the site plugin must be available, and an active Self enrolment method must exist in the course. Dates, keys, capacity, roles, and account state can still prevent enrolment.
Removing a Calendar block changes one page layout; it does not erase Moodle calendar events. Identify whether you are editing Site home, your personal Dashboard, or the default Dashboard before making the change.
In Moodle, Teacher is normally a course-scoped role. Enrol the account from the course Participants page, choose the least-privileged teaching role, and verify the resulting access before classes begin.