Surface RT stuck on "Surface" screen, RED LED on PCB blinking forever.

RED LED on PCB near left microphone lights immediately after power button press for about 3 seconds then starts fast blinkink forever, together with "Surface" stuck screen. I did not found any information about this RED LED, this is probably totally unknown diagnostic item for Surface RT community.

Have anyone some idea what the 3 sec light + blinkink forever of RED LED means?

And how to fix it?