So how exactly are you formatting your SD? It's very important to format it correctly, create FAT32 partition and copy MLO in one go. The boot ROM also seems to not like large FAT partitions, try with a 64MB FAT32 partition or so.
It also probably lost it's charge over all that time, you should connect a charger and give at least 15min before booting (pre-charging is done by hardware and doesn't need any loaders).
Other than that I've never seen anyone losing their NAND just by overloading USB host, you might as well have simply fried your board. You can probably unscrew the back and check for some fried parts.