Its impossible to boot Windows 10 using the windows 8.1 bootloader but most likely it works vice versa.
For those who liked the pre 9926 start menu better, add this value to the registry and restart Explorer: Code: HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\EnableXamlStartMenu - DWORD 0
Well, it seems that after installing VirtualBox in this build the program doesn't work AND it screws up your system (just like in build 9901). Time to reinstall! (again...) PD: Also, i went into safe mode and the start menu and the tasklist on the taskbar don't work! (that's weird...)