[Peter Sartwell]

Just googling using your error “2MEM/1/4: SODIMM1/J23REVERSED” suggests that your RAM may be to blame. RAM is relatively cheap and easy to replace.

That said, you can try to simply remove the RAM, wiggle it in the slot to clean the contacts, and put it back in.

Or, if you have two sticks, try running only one at a time with AHT to pinpoint the troubled stick. It may complain that you only have one installed (where the OS really runs best with both).

If you haven’t done a RAM swap before, beware- it takes some precautions to avoid harming the RAM or other components.

Ifixit and other sites have info on how to do this, just google powerbook g5 ram replace and you’ll get close to the how-to’s.