Maybe your hard disk or SSD was intact but it failed to boot due to certain
misconfiguration of the boot firmware. (You said that you've made certain
modification to the boot firmware and it no longer boot from internal hard
disk/SSD.)
Because libreboot hasn't been updated or maintained for a long time, and
since the libreboot project leader has bankrupted and therefore is unable to
provide much help (documentation), the best option is to re-flash coreboot,
which is under active development and well supported.
Since you already have libreboot, the write protection (an anti-feature
imposed by the OEM in order to prevent users from modifying firmware) is
gone. You can try to flash coreboot under Live environment to revive your
computer. I have just asked one of the contributors of coreboot, so I'm sure
that it is possible for you to flash coreboot without disassembling your
computer and using an external computer.
See documents on coreboot.org for more details.
