Installed the 64bit Enterprise of Windows 10 on it's own 320GB HDD, all other HDD's disconnected. After the restart, I was reconnectd one after the next HDD's, 4 of them OK and cam to the 5.: BOSD! That 5. HDD is the system HDD with Windows 8.1 Pro on an 1TB HDD. Restarted the machine and used the BIOS Boot Manager to chose the old 1TB Windows 8.1 Pro HDD and that just worked fine and booted as normally. Restarted again and chose the 320GB with Windows 10: BOSD! Now I'm back on Windows 8.1 and transfer all relevant data to anb new drive which will need 1 more hour and will than disconnect that drive again and start Windows 10. It's for a long time the first time I was get an BOSD again. What could be trigger that? Anybody has any idea? Thanks.