Did I brick my flashcart?

So I am not sure what happened...I am using an R4III Upgrade and it has been working fine with YSmenu and loads most games. For some reason all of a sudden not all of my games were visible through the DS. I loaded a folder named Games with subfolders of each game and then the .nds files inside (/Games/Pokemon Black/pokemonblk.nds for example), this worked fine usually but suddenly I couldnt see any games alphabetically below Star Wars, even tho when i connected the card to my computer i could see all the folders/files. So I tried reformatting my drive and reloading everything and now I cant even load the firmware, it just freezes at "Loading..." everytime, reformatted about 8 times now, could I have screwed up my actual flashcart somehow or is it the SD card? No clue what to do...

I dont get it, I mean the files are on the SD card just for whatever reason the flashcart isnt recognizing them at all, Ive been formatting it as MSDos (FAT) on Mac OSX using disk utility, is there another way to do this? Also I just realized thsi started happening after I tried to "write Zero's over the data" and about 85% through that operation I got an error, could this have screwed up my card somehow?