Sounds like you've got a bad RAM chip. Are they socketed or just soldered in?
Ah, bummer

Socketed. I tried reseating them but to no avail.
You get 2 MB from 4x 514400 chips as far as I can count
Really? Doesn't the name (HM514400BZ7 1Mx4 DRAM) suggest that you get 1MB per chip. 4 chips, meaning 4MB?