[Help] Possibly Bricked LG G3 D855

My LG G3 is and international D855 and is unable to enter recovery, with the phone going black after the twrp logo shows for a few seconds. The phone has no OS installed because I was going to flash a custom rom so there are only bootloops when booting up the phone. Entering download mode is not any good either because a message appears saying secure boot error and the phone goes black with only the LED flashing Red and Blue, I tried going back to stock with fastboot but in the process I lost the ability to enter fastboot, is there any hope :(
I'm hoping somebody can help and I would be extremely greatful, Cheers

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