Some ESP8266 might have some Firmware installation problem. We can use Arduino board as Serial Port testing tool to send Serial command(AT commands) to ESP8266 and do trouble shooting:

Step 1) If your WIFI Shield is inserted on the UNO board, please remove the shield from Arduino board. Also please remove all the jumper caps on the WIFI shield if any.

Step 2) Connect the WIFI shield to Arduino board by jumper wires as following:

Wifi Shield E_TX Arduino TX(D1)
Wifi Shield E_RX Arduino RX(D0)
Wifi Shield 3.3V Arduino 3.3V
Wifi Shield GND Arduino GND
Arduino RST Arduino GND

Step 3)Connect Arduino to your PC with USB cable

Step 4)Select UNO board and Port as following:

Step 5)Open Serial Monitor (no need upload any code)

Step 6) In Serial Monitor ,select  115200 baud rate and Both NL &CR  as following picture, then type AT and click Send

Step 7) Now your serial monitor will see AT OK as following picture:

If after Send “AT” command but your Serial monitor does not show “OK”, please change to baud rate to 9600 and try again.