2. For Hardware-
when a dead phone not possible to repair only with software you need to repair phone hardware.

Which hardware you need to check for dead phone-
(1) when you try to flash though phone not boot check power source/battery voltage/V+ pin in phone connector. just do confirm phone found enough voltage for software operation.
(2) though phone power source is ok but still not boot, do confirm your tx and rx is 100% working/tested.
(3) though tx rx is ok, than check your phone connector, its tx rx pin is confirm connect with cable and internal connector pin is joint on pcb perfectly.
(4) though pin is ok, maximum china phone tx rx going to cpu after crossing a resistor or capacitor so check them.
(5) though resistor is ok now you need to check boot diod, all phone have no boot diod so last try is check cpu tx rx pin.
(6) though boot is ok but phone not receive flash file, maximum time this problem coming from flash ic or ram (maximum china phone flash memory and ram have in one chip). so you need to try first re-hot it though not solve change it.
but its true flash chip/ram always show error not only for them, sometimes cpu to flash chip/ram connection lost for bad cpu pin or bad cpu soldering on pcb. so check both of them.
(7) phone flash ok but not power on (although file is 100% correct) , for it you need to check

Flash chip/ram (95% include in 1 chip)
Clock crystal and battery
26mhz (near rf ic)
Rf ic,
Power ic and v+/b+ way
Bt ic
Last try is cpu.