Scratch HD? So you don't care what is on that HD? You can use EETech utility (BartPE or standalone) to remove encryption, or at least restore original MBR.
That should allow you to reinstall OS. There are also some other utilities to wipe disk, like Ghost gdisk.
if you don't care about the data, just fixmbr it. A reformat won't help though (that does not touch the MBR).