Ubuntu is stuck on login screen with no input keys working, including power button

I had a problem where ubuntu was restarting automatically after poweroff. I added

GRUB_CMDLINE_LINUX_DEFAULT="acpi=noirq quiet splash"

To /etc/default/grub according to this answer. After shutting down, it still rebooted, and now I'm stuck. I've tried long pressing the power key, pressing ctrl+alt+F3, but nothing works. Please help me.