My bet is that the "HP Update" delivered today corrupted a portion of the laptop's firmware. The original hard drive probably has a recovery partition that an uncorrupted area of the firmware was able to look for and boot; once booted, the recovery partition checked and rewrote the corrupted area (the "Flashing boot block" bit).

Hard to tell why the update would do that without information we don't have. Could be anything from a bad download plus poorly-written integrity check, to the update expecting exact OEM hardware integrity. Both would be bad decisions by someone at HP.