Hi,
I know you said you tried flashing the firmware already but just in case:
-try using the sd card that came with the printer or different sd cards until you find the one that works (try using small capacity sd cards <1gb or less)
-did you format the SD card as FAT32 ?
-make sure you have the 4 proper files in the sd card (diy_icon, SYSTEM, .bin and .txt files specific to your machine)
-usually nothing displays on the LCD during update, did you give it enough time?? 2-5 minutes
-unplug power cord from the machine for a few minutes and try flashing again
-Its usually a soft brick when using wrong firmware files , meaning you can recover from it. Just keep trying. Good luck