I have found a similar qustion to mine but there was no good response.
I've connected my ESP8266 to Arduino UNO.
Then I got some trouble with software serial communication with Arduino and decided to change baud-rate to 9600 (previously it was 115200).
I used AT+IPR=9600 command to change it.
After that blue led of esp stays on and not taking AT commands any more, but output some gibberish to serial monitor.
Note: I connected the esp8266 through a voltage regulator and a power source and both gave the same problem. My firmware is supposed to be updated so I don't think that it is the issue.
Could anyone please help me?