Can't boot up a machine with replaced memory cards

I bought and replaced some new memory cards (PC4-25600) for a notebook PC (NEC, purchased in Japan) already running FreeBSD. The RAM cards fitted perfected into the slots. However, upon turning on, FreeBSD does not boot up and the screen is blank. I don't think it is even getting through the BIOS. Is it possible that the BIOS/manufacturer can "lock-in" the memory cards? Or is it a problem with FreeBSD?
I would suggest you look at the RAM modules you replaced.
Make sure that the speed is similar to your replacement modules.
PC4-25600 might be too fast or unsupported.
What are the old modules speed? Post a part number for old modules if unsure.