I bought 4 GB of memory for it. G.SKILL FA-5300CL5D-4GBSQ.

The laptop came with a 512 MB stick of apple memory and some other cheapo made in korea hynix 512 MB stick.

Those work fine.

The 2 GB g.skill sticks, both work fine. I can use one by itself, in either slot.

But when I put them together, I can't use the computer. It turns on but nothing comes on the screen.

I tried swapping them to the next slot, and they don't work.

The computer is fully functional with either of the two sticks installed.

What is going on?

Is there some 2-3 GB limit on memory for this model? too old or something? What am I missing?

It's a 2.16 GHz macbook pro, before the LED screens or the no firewire 400.

If it is the same Macbook Pro as me which is the 2.16ghz Core Duo type then its only limited to 2gb I think.

Only the Core 2 Duo's support more than 2 GB.

The Core Duos are limited to 3GB.