Troubleshooting RAM is always problematic.
First question to ask is; was the RAM purchased from a reputable company or was it purchased because it was cheap.
I see you have the same problem with a G5. Was that the same RAM or different RAM - same supplier?
There was a period there when Apple tightened up on the specs for RAM in their machines. They did not change the specs, just the tolerances that the machine would except.
Some resellers never did get over the shock and still sell stuff that does not meet the specs.
Put the old ram back in. How many sticks do you have of the old stuff?
Boot the machine, see if it recognizes the RAM.
Continue to add RAM and check.
It is all trial and error, adding/restarting/subtracting/restarting.
Does the RAM have a warranty? If so, you may just be about to use it.
I'm trying to install 512 MB sticks of RAM into a G4. It seems to recognize the memory sticks inconsistently. I had three sticks, it only recognize two. I switched the slots then it read one stick but not another. Does anyone have any troubleshooting tips?
Same thing is happening with a G5 except with larger capacity memory sticks.