Kurt Ullman writes:

The cable that attaches to my garage door and then to the pulleys has
come off and wrapped itself around the bar or whatever it is that the
pulleys are attached to at the top.

This is typically due to insufficient winding of the springs. In that
situation the springs go limp near the top of travel, then the torsion is
off the bar and thus the tension is off the cables, and the cables flex off
the drums. If it was working OK before, and nobody touched it, it is
likely that the setscrews on the spring-winding cones, or on the drum,
slipped on the torsion bar.

Is this something an amateur can try to fix?

Depends on the amateur. Someone else posted a link to my page.