Chkdsk saves the day again!   Encountered this error on a Dell laptop today.   The suggestion from the MS Knowledge base was to restore an older version of the registry :

However I found when I tried to copy out the software hive that it was unreadable and couldn’t be copied.   

After running chkdsk /r  (from recovery console) it found errors and corrected them.   After that – the laptop booted fine!

I still suspect the disk may have a hardware fault, however at least it’s in a state when files can be copied off – prior to an impending disk failure/reinstall.