Okay, so your car still starts with a jump? Then only 2 things: Battery is totally dead(did you try taking your battery and putting it into another car yet?), or you might need to actually CHANGE your ground. I couldn't really grind down the area where the ground was connected, so i just grounded the battery to the rear passenger shock tower by connecting it to the strut bar(since my battery is in rear). Ground is perfect now. Oh, and try cleaning your terminals and make sure that the wires are in there nice and snug, and clean your posts too. If all that still fails, then shit, I have no f-ing clue what could be wrong, other than a broken ass starter.
OOOOh my rex didn't wanna start after I kinda blew the old engine. It started to knock pretty badly, and when I was driving one day I heard a loud "clank" and the car died about two seconds after I took it out of gear. I have no clue what it was, and I wasn't able to start it but once, and it did that same "clank" and just died. After that, nothing . Hopefully that's not your problem.