Old / New G5 issue..Memory slots showing as blank

[hal]

I think the same thing happened to me when working on a mac pro. I took the RAM tray out and took a close look. There was a gigantic dust bunny in there. Blew it out and all was well. But there is a chance that the reason your G5 was up for sale was that it had bad RAM slots and the seller was hoping that no one would notice...