Took the back off the G5 PowerMac to install new RAM. Removed a pair of 256 MB modules & replaced them with a pair of the new 2 GB ones. Computer failed to boot, this indicates a RAM problem. So I removed the new RAM & replaced the pair of 256s. It booted but didn't see the restored pair of 256s, only 6 of 6.5 GB registering. Me not understand. I'm giving up for the night, might tackle it tomorrow. It won't even boot at all now & all I've done is refit RAM.