Soft or Hard Brick my Lg G3 D855

hi, guys i recently bought lg g3 d855 on ebay. my lg g3 d855 came installed version with anroid KK. i tried using imageprepGUI. now the phone cannot enter download mode nor boot into system. i is getting continuous boot loop after lg logo. i can access the factory reset menu by pressing volume down and power button also the phone is not being detected on my computer not even is QDLoader 9008 mode.
please help me out, i have been searching and searching for the answer but have been unsuccessful.

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