I was having problems sending MMS, so I tried re-downloading & re-flashing, as has been suggested, and now my GS3 is effectively a brick. Idunno what happened, I wiped data, cache, dalvik cache & fixed permission, then flashed the rom then gapps like normal. Now if I try turning it on it flashes the Samsung logo for half a second then turns back off. Same thing if I try to boot into recovery. If I plug it in it'll still charge & I can see the charging animation, I just can't actually turn it on to anything.
The only thing I can do is go to download mode, but since I'm on a Mac I can't use Odin. No clue what to do...