If i well understand, you have only changed the system bord on this computer, with the same model.
It is the only thing that you can't do directly. Windows 8 check for secure, that there is no change between your OS, and the secured keys that are stored on your UEFI of your original system bord.
What I suggest you, is to test the boot with a Linux live CD (without secure boot if needed : I don't know exatly if Secure Bood is actualy compatible with all Linux versions), to be sure that your PC is OK. Ask to Fujitsu if it is possible to activate this new system bord because, I don't know how to do that, if it is the issue that I have discribe you