I've got a 1.5GHz 15" PB and I installed an additional 512MB of RAM from crucial shortly after I got it (last summer) and I recently noticed that in the system profiler it's only reporting one 512 stick. Interestingly enough the one it's showing is in the upper slot, the lower one is reportedly empty, which is where the apple stick was. I haven't been able to open up the RAM door to see if it's seated correctly, (I don't have the right size screwdriver) but I was wondering if anyone here knew why it might have disappeared, and what problems this could point to. What kind of problems are common related to disappearing RAM on a PB? Thanks for your help.