I can get the pendrive to boot in Legacy (aka BIOS) mode, but I can't get it to boot in UEFI mode.
When I attempt to boot in UEFI/Secure mode, it complains before Grub even starts.
If I boot UEFI/Insecure mode Grub starts, but the machine freezes immediately after attempting to boot the OS.
By editing Grub's boot entry to include echos in stategic places, I have been able to establish that Grub does indeed manage to load both the kernel and the ramdisk into memory, and then the machine freezes.
The freeze happens regardless of whether I use nomodeset or not. I even tried noapic and nolapic and acpi=off (blind shots, I know), to no avail.
I found quite a few similar questions around here, but no answers that would help me further.
I was able to install Ubuntu to the disk from the pendrive in Legacy mode, but for some reason I can't boot the disk installation: grub starts, but it doesn't even get to the menu and drops me to the rescue prompt.