Hello everyone i iave lg d855 while flashing battery died and after that screen gone black but pc detects it only shows qualcom in my computer manage screen is black
Welcome to Android Central! Are you saying you were flashing a ROM? If the battery failed in the middle of the flash, I'd guess that the phone is completely bricked.
The LG G3 is a device that was released over 7 years ago and only capable of running 6.0 Marshmallow. Most likely it will not be worthwhile to have it repaired at this point. You will be better off purchasing another device that is up to date.