I've been using this R4 for over a year, and it was working just yesterday. The only thing I changed between when my DS was working and when it wasn't is that I put Summon Night Twin Age (from a previously reliable provider labeling it as release  Summon_Night_Twin_Age_USA_NDS-XPA) on my SD card, after trimming and scanning it with NDSTokyoTrim. When I started up the DS, it said it couldn't see the SD card, which I'm used to occasionally since having to remove the spring from the R4 when it got stuck and wouldn't hold the card inside. When I rebooted the DS, it wouldn't turn on. ANother odd symptom is that when I plug in the AC adapter, the yellow light turns on for about a second and then stays off. Even with no carts plugged into either slot, it still doesn't respond to the power button. I also had a DS with broken shoulder buttons laying around to test, and the R4 with that SD card did the same thing to it.