In a healthy device (or even a 'bricked' one that can far enough into the boot process) you'd see 'Loader' or similar message on the screen like what you see when it's flashing firmware in preboot or from a gupdate.gcd file.

There's one other thing to try seeing it can access preboot and that's by using a modified boot.bin as an RGN to force it to read the SD. I've got other priorities presently so i'll make it for you later today or you can do it yourself if you don't wish to wait, Post 33 here: [Only registered and activated users can see links. ]