OK, this is where it gets very difficult to diagnose.
It sounds as if the sequence wheel - or something working with the wheel -
has been dislocated or broken.
The usual problem with this model is the tonearm not lifting after ended play
but this fault usually results in a permanently lowered tonearm rather than
permanently raised.
The fact that the platter keeps spinning tells us that it's probably not an
electronic fault or a fault with a stuck key on the panel - which brings me
to asking which of the two different models of the Beogram 2400, you have ?
One has a completely square dustcover with all operating features under the
cover, the other has a sloping front with all buttons outside on the front.
Martin