Sorry, i am afraid i cant help much. However, i have had this problem. My 65 gallon, at one point in time, became a death tank. The fishes looked healthy one second, dead the next. I had no idea what to do. I even considered giving up the hobby. Then i posted here and tonnes of guys helped me out. Turns out it was a bacterial infection, triggered by the recent warm temperatures.
Maybe you have the same thing, could you tell us your tank parameters, like ammonia, nitrite, nitrate as well as the temperature. You seem very anxious, dont worry, give it time, someone who knows what to do will post when he/she comes along.
Keep strong dude

P.T.