There if I remember correctly, are instructions for installing MBX 4.5 with Windows 10 on the Janome website where the downloads are...You may also need to get the dongle update in order for it to work...the instructions are very precise...I installed 4.5 on Windows 10 awhile back but it was an upgrade not the full version....The instructions for installation are probably different for the full version of 4.5 as oppose to the update...Not sure which you are doing...I have since upgraded to Version 5 and also use Windows 10 which no longer requires a dongle..
I hope you get this worked out soon. Have you looked at the instructions on the janome website?