This is a recent installation which appeared to be working just fine. While sorting out some teething troubles with ESP-IDF I got a warning about some update failure - no details - and then nothing seemed to work. I'm guessing automatic updates in the background. Pretty sure I wasn't doing anything controversial. Upon rebooting I briefly see a message that "sda4 is clean" and then a flashing cursor forever. I have tried CTRL+SHIFT+F1 but this does nothing.
Is there any way to recover this? I have an nvidia graphics card, as that seems to come up in similar questions. I guess I can boot from the DVD again, but hopefully can avoid re-installation.