Can you get into the BIOS? This page seems to think it's "Cmd"/"Opt"/"O"/"F" all four at the same time.
If it's like any other Intel BIOS, it'll be an ultra-simple menu -- no mouse, just arrow keys and Escape and Enter and not much more. Look for "Hardware" or "Memory" or something, then see if the slots are activated, iActuated, or whatever the Apple term for it is. (They may or may not have written their own firmware.) I'd be happy to talk you through it if want handheld, we just need to set up a time.
Oh, hey, look, when I research the topic, I get you over here.