Post FTM Does not work (blade III)

In my ZTE Blade 3 stopped working download mode (FTM). Do not respond to the switch, connection for charging, turning tybu FTM (vol- + USB | vol- + vol + | etc. ..) not charging LED lights up, the computer does not detect it. mistakenly been installed bad software. Can it still be saved, or do I have to replace the motherboard?