Help my g3 d855p died

I have lg g3 D855 i flashed wrong rom, so now my device died :crying::crying::crying::crying:

i try to flash stock rom but the phone did not enter download mode and the screen is off too and the computer detect the G3 "lge androidnet usb serial port"

So any idea or method for how to fix my G3 :crying::crying:

Tablet died in less than 24 hours!

Ok so got my shiny new s2 yesterday. Set it up fine then noticed this morning it was continually rebooting itself. Eventually it booted and just as I was typing something the unit froze. I turned it off by power plus volume down. Now it won't turn on at all. Completely unresponsive. Very annoying. It is currently on charge even though battery was at 85% when this problem arose.

The tablet is the 8.0 LTE variant. Any suggestions before I send it back?

Cheers!