To deactivate P3Dv4 and P3Dv5 just uninstall them. You don't need to deactivate FSX (but you could uninstall it anyway (see my note at the bottom of the post)).

I recommend that you uninstall all Captain Sim products because some, if not all for P3Dv4/v5 need to be deactivated. You use the ACE to deactivate them. I know it's a PITA, but it was better to be sure than sorry.

Note. If the new motherboard is a different type to the old one (including getting a new Chipset and CPU), I'm sure you will need to do a reinstall.