Act of God. If you live in the UK then you should know R4's are illegal and the Queen and her ministers have been making incantations to destroy all DS using R4.
Actually, I have no idea. My guess is probably some kind of corruption in the onboard non-volatile storage area, aka, bricking. If you had a programmer device and a JTAG cable you could probably open it back up and un-brick it.
EDIT: as for cause, could be anything from a maliciously modified ROM to improperly seated contacts to complete fluke. Also a possibility- recent Nintendo updates which detect the presence of R4 and consequently kill your DS, which has been threatened by them in the past but AFAIK never carried out. But you never know.
Last edited by arfink (Aug 10, 2010 5:24 pm)