The bootrom may show a blue screen with yellow text if it fails to find a suitable firmware to boot into. The most common reason this might happen is due to all firmware partitions being corrupted.
Example text
BOOTROM 8046
ERRCODE: 00F800FF
F8F8FFFF FFFFFFFF
00000000 00000000
Fixing
If this is due to a software problem such as corrupted firmware partitions or corrupted NAND header, this can only be fixed with an ntrboot-compatible flashcart or a hardmod.
If this is a hardware problem such as a faulty NAND chip, you most likely need to replace the motherboard.