Grub2 not booting initrd

I have a laptop (with UEFI) that used to be able to boot from a usb stick, but can't any more. The problem started when I interrupted a fresh install of Devuan Live. The laptop has a non-removable mmcblk device and a removable (real) hard disk. Both have several linux kernels on them (Debian, Ubuntu). At power on I get the usual grub2 menu, but whatever I choose: it loads the kernel, then the initrd, but then nothing else happens. If I just load a kernel (no initrd) and boot, it starts booting but halts with a kernel panic (VFS syncing problem). memtest won't boot either. What could be the source of problem, and is there anything I could do to save the laptop? The only tool I have on the laptop itself is the grub2 console. Otherwise I could move the hard disk to another PC, put something on it, put it back in the laptop and try to get it booted.