Starting issue

I’ve had charging issues in the past with this car I tested my battery it said bad battery, changed the battery, battery light was still on. (Mind you my car still started) Had somebody Change the alternator (it still started before the alternator change) there were some sparks that flew but before he started taking off the alternator he disconnected the positive cable from my fuse box underneath my hood. (Don’t know why he did that) as he was taking off the alternator the last thing he took off was the positive cable at the back of the alternator by the pig tail, there were sparks that flew as he was taking off the positive cable to he alternator as I mentioned before so we finally got the new one put on and now my car will not start it did start but immediately shut off it felt equivalent to running out of gas. My lights on my dash came on and then everything went dark on my dash can someone please explain what is going on with my car the lights will come on when I lock and unlock my car but my car won’t start.