Hey there, @Bluetech!
I'd definitely agree with @Ralston18! Even if you do have an identical model/brand motherboard, you will still need to re-install the OS itself onto the SSD. Keep in mind that clean install onto a primary drive requires you to disconnect the secondary HDD from the system, otherwise you might encounter an OS confusion which would cause further booting issues. I'd advise you to use the SSD for a primary storage (boot) as it would give you much better performance than the mechanical hard drive.
If the mobos are different, you might actually need a new genuine Windows install altogether or at least a new activation code. For more details on this, please refer to MS support on their official website. Here's a great...