After the POST screen, it doesn't load Windows, but instead just displays a black screen with a blinking cursor in the upper left corner. Based on past experiences, there's almost no real fix for this. It's one of the reasons that I'm so fanatical about doing clone backups, because all I can do when it happens is to roll back to the previous clone. The non-booting drive is readable as a non-booting device; that is, if I swap in a bootable drive (usually the previous clone), then connect the non-booting drive as an external drive, I can read everything on it, so as long as I have at least one bootable drive, I can recover my data, but it's very time consuming! It takes 30-60 minutes to copy my documents back from then non-booting drive, then about 2 hours to clone the bootable drive back into the non-booting drive.
I've run virus checks. I've run CHKDSK. There's no virus and no disk errors. I haven't tried FIXMBR this time around, but it's never worked before when the problem happens.
Based on past experience, I may end up (again) having to roll way back to the nearly-as-shipped configuration (which I keep on a separate hard drive in a fire safe), clone that into another drive, and use one of the readable backups to reinstall all of my software. And then it will (probably) leave me alone for a few months before the problem starts happening again.
This is very frustrating. At least I did bring the backup drives and hardware, and I have multiple computers, but I wish I didn't have to have triple backups just to make sure I have one working computer!