I'm guessing you're running a 1GHz, 1.25 GHz, 1.33 GHz, or 1.5 GHz (first model 1.5) 15" PowerBook. The Nanya (or what they have pictured) RAM is not certified for use on those models because of their pickier memory controllers. I mentioned this in another thread about RAM in a 15" 'book. I had a similar experience when I owned a 1.25. Their (more expensive) Samsung chip IS certified for use on those older Aluminum machines. Assuming your machine is properly functioning, I would say your RAM is probably not matched for the CPU.
If I am wrong in any of my assumptions, then please ignore this post.