Is the upper thread threaded correctly?
The upper thread must be positioned in the thread guide on the top rear of the machine and lie correctly in the tension discs and in the thread take-up lever. This moves up and down on the front of the machine. It is best to hold the thread lightly in both hands so that you can feel whether the thread is threaded correctly at each point.
Especially after a thread break, it is easy to forget to raise the presser foot when rethreading. However, with the presser foot down, it is easy for the upper thread to be positioned incorrectly in the tension discs. The upper thread then has no tension and is pulled inside the machine the first time the needle moves down, where it gets caught.