I have a MCX2 and my local HS sold me a new mainframe because mine was broken. the screws are really small in the thing. i finally got the whole thing reassemeled and went to do a test flight and I gave my heli throttle and all it did was spin in circles and go all catastrophic on me. I dont know what to do. I think it has something to do with the trim.
please respond asap

It could be that when you reassembled the frame of the helicopter, one of the big gears connected to the main blades is not lined up correctly with the pinion gear on the motor. Its been a while since Ive worked on an mcx but check to make sure your gears are properly aligned and spinning the blades.