If you cannot even access the hard drive with a USB boot, I think there is really only one option left, and that is to completely reinstall Windows. I've been going through various Microsoft pages trying to find something else I could ask you to try, and in the end, we have already tried the ones I see there.
I also found one thread on the Microsoft forums where a lady with an HP computer tried using multiple Windows discs that HP sent her to reinstall Windows to the hard drive without formatting the disc, because she had 300GB to 400GB of data on her hard drive that was not backed up, and she said she could not lose those files, and in the end, the only way she could regain access to the hard drive was to reformat the drive during the installation process.
I wish I had a better way to resolve this, but we have tried everything that I thought might help, short of reinstalling windows.