ESP8266-12E MicroPython Unable to access REPL (Python prompt)
I was having a similar problem with a Wemos D1 mini board. Erasing and Flashing the firmware worked. However I was getting no REPL prompt, resetting was giving me garbage. I solved it by adding "-fm dio" when writing flash.

esptool.py  --port /dev/ttyUSB0 --baud 460800 write_flash -fm dio --flash_size=detect 0 esp8266-20170823-v1.9.2.bin