I have a WD 5TB USB drive with backups on it, which I've used for about 9 months (single partition: there was a thing I had to do to overcome the 2.5TB limit that made it incompatible with XP, forgot what but it was about the partition table). It's not bootable; my BIOS is set to first boot from USB, then HD. For 9 months under W7, there has been no problem: the drive was plugged in, the computer booted from the HD, all was well.
I just upgraded to W10 Pro 64, and that has been okay for about a week -- this included a half-dozen reboots (I think the drive was not attached). I then plugged the drive in and did a backup to that drive; no evident problems (so now W10 knows that this is my backup disk). However after I rebooted, I get a black-screen message at boot-up "Invalid Boot Partition" and that's as far as the machine will go. It's fixable by unplugging the USB drive (it boots from HD), and the drive works after plugging it in.
I assume the problem has to do with the USB drive. Is there a way to determine what, exactly, is invalid or which partition table is invalid (I'm just assuming it's the one on the USB drive)? And a follow up would be "and how do you fix it"? If anyone has any idea why this happened, please clue me in.