I applied the upgrade to Windows 10 to my Win 8.1 system. I want to go back, but MS have dropped something on the system here preventing me from loading 8.1 again from my original install disk. Presumably something in the registry. What or where is this flag, anyone know? What I want to do is install 64bit Windows 8.1, it currently has 32bit. Following my rebuild, I want to be able to use the 16GB of RAM the rebuilt system has, while the 32bit system only allows me to see 4GB.