If, being of a tidy cast of mind, you used the pair of 100ns, they are too slow for the 475, no matter that the slower LC can use 100ns. You could hazard using the two faster cards, which would allow the the System to treat them both as 80ns, with a very good chance that they would work. (Ideally, you will use two completely-matched VRAM cards of 80ns or faster.) If that does not get you going, it is more than possible that you have a separate problem from that of the VRAM specification, relating to the VRAM slots, your PRAM battery (because the video characteristics for the display last used are stored there for the startup process), and so on.
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