[Q] Kernel crash, can't go into download mode topic

Hi,
I recently bought a G3 and 3 days ago i downgraded to kitkat to be able to root, I also installed CM12, it was fine until I had bootloops so I reinstalled it and yesterday my device had a kernel crash.
I wanted to go back to stock G3 but couldn't reach download mode! Even after a kernel crash and selecting "launch download mode" it crashes.
I don't know what to do, do you have an idea?
Thanks!