Yesterday I noticed that my (15" 1.5 GHz 1 GB RAM) Powerbook only thought that it had 512 MB RAM when I looked in "about this mac". Upon looking further in the System Profiler, the lower RAM spot was reported as "Empty" and my top RAM spot was working fine. Nothing like this had happened to me before. I powered down and pulled out the RAM to inspect it - and it looked fine. I had expected bad RAM to prevent my computer from booting up entirely rather than not showing up in System Profiler. Note - my lower spot had 512 MB original Apple RAM and my top spot had a 512 MB stick from crucial.com. I put the RAM back in thinking it was a connection issue, but System Profiler still didn't recognize the lower RAM. I then powered down again and put the crucial ram in the lower spot and the Apple ram in the upper spot. Wah-La, everything work again after the switch and I see the correct 1 GB RAM listed. Weird. Anyone else had problems similar to this with a Powerbook not recognizing RAM? Specifically with the lower RAM spot? Any idea how I can prevent this from happening again?