I have a 15inch 1.25 Ghz PowerBook (the first aluminum vers.) It has an original Apple 256meg RAM chip and a Replacement 512meg RAM chip in the upper slot. The other day I noticed my comp running slow and after some investigation I noticed that it was only showing the chip in the top slot and not the bottom. I opened it up and pulled the chips out reseeded them and it worked. THen it froze after 24hours usage. When I rebooted it only saw the upper slot again. Then I switched the chips to the otehr slots and rebooted. Same thing. It worked for a day and then frooze. Upon reboot, it only saw the top slot (this time the 512 chip) Anybody know of RAM slots going bad? Each DIMM seems to work fine in the top slot, but nothing stays stable in the bottom slot. I want to avoid sending it in to Apple if at all possible.