(just an idea) as soon as it happens, what does dmesg say?
I dont know. I will test it next time it happens.
Maybe the manual eject button is stuck (yours is from an older broken PC as mentioned)
May just wait at GRUB or/and at different break-points and check this first.
Or just remove the data cable from drive and check this?
I would do this.
The DVD drive is a new one. The hard disk is from the broken PC.
I will check the cable.
Thank you both