alienware shows power light and keyboard, screen stays blank

I have an old Alienware computer (model 15 R3) that I use for testing. I installed Ubuntu 22.04 on it and it was great for running CUDA jobs. Now after running the Phoronix test suite (or the latest upgrade with APT, both happened) it does not start any more. Nothing is shown on screen in terms of BIOS, grub or the Alienware logo. The Power light is backlit and does come on, then goes off and back on again, after which it stays on. The keyboard backlighting also shows, and I can see that the screen is blank not off (it is lighter than when the power is turned off, but nothing is shown). I've r

Question by alle_meije on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.