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Important things to resolve your problem (Sim Card) ..If you know exactly what sim you have it will be easy way...
But you said your box Genuine and sim not removed So maybe original sim (Dream multimedia a8p)
In this case follow this link and do (Null modem cable only without Network lan) and flash original bootloader from here download last bootloader for your sim
But you need to use Loader LD2 and this software not free for genuine (should by have pro key) you can get it by make donate..
P.s: Your box is DM800se so should by use both cable to gather (mini usb+lan)
But you said your box Genuine and sim not removed So maybe original sim (Dream multimedia a8p)
In this case follow this link and do (Null modem cable only without Network lan) and flash original bootloader from here download last bootloader for your sim
But you need to use Loader LD2 and this software not free for genuine (should by have pro key) you can get it by make donate..
P.s: Your box is DM800se so should by use both cable to gather (mini usb+lan)