I have an 8 month old 15" 1.33GHz Powerbook with 1.5GB of ram. In the lower memory slot there is a 512MB PC2700 sodimm. In the upper memory slot there is a 1GB PC2700 sodimm. I noticed today that the lower memory slot is showing up as empty in the system profiler so it looks like I have only have 1GB of ram. If I swap the memory so that the 512MB is in the upper slot and the 1GB is in the lower slot, the lower slot still shows up as empty and system profiler repors I have 512MB of ram installed. Both sticks of ram work fine alone in either slot. Last time I can remember system profiler reporting that both slots were occupied was about three weeks ago. I dont know what would cause them to suddenly stop working together. Anyone else seen something like this?