Asking here too:
I had been using Windows Insider on my SP3. I've been on Windows 10 build 10240 for the past week or two (whenever it was released), under the impression that this is the RTM build.
Like most people, I did an upgrade over W8.1, but with W10 releasing today, I wanted to start "fresh" and get the full, new experience while hopefully cleaning out any issues that may have arisen over the past month of new builds, upgrades, etc.
So I chose to Reset my PC. It prompted my SP3 to reboot, which it did, but now it's stuck in a loop. It reboots to an error screen that says to reference this error "INACCESSIBLE_BOOT_DEVICE".
Everything I've read indicates I'm going to need to hopefully launch into a recovery mode and likely need to format the drive. However, I'm not sure where I should go from there--will I need to install Windows 8/8.1 on my SP3 and then upgrade to W10?