Default [Q] help phone wont go into download mode

ok ive cracked my screen and my power button works half the time so i am going to return it to verizon but im rooted so i need to flash back to stock when i try to go into download mode it comes up i hit up to continue and then the phone turns off so i cant flash to stock and recovery seems to work fine and so does the rom. how can i flash back to stock through download mode? i could use recovery but id rather use odin thanks in advance

samsung galaxy s3 verizon running jellybeans rom