Hmm, that indicates it’s at least starting to boot but never finishing or running into error state. I see this sometimes if I load a bad kernel/initrd, the boot loader thinks it has booted but the kernel panics and it doesn’t proceed further. It’s possible to get into a similar state without messing with the boot files if they somehow got corrupted on their own. It could also be a problem with the actual board/bootloader.
What have you tried so far? I’d start by unplugging it for a few minutes.