esp8266 based wifi modules extremely cheap, easy to use but also too fragile. you can easily make it unresponsive to commands by updating it via cloud, changing baud rate or using tx & rx pins as gpio.
i purchased one just for testing it's features and bricked it with AT+CIUPDATE command. well, actually "bricked" is wrong word in that case, it's still alive in most cases but just stucked in loop.
there is a lot of entries in web about reflashing it but almost all of them demonstrated in linux variants. this instructable tells how to restore default firmware in windows platform.
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Step 1: Wiring and Gathering Tools
+ first you have to directly connect it to your pc by using a usb-ttl or serial-ttl adapter. i used an arduino uno by removing the atmel chip. you can check out this instructable first for how to do it.
+ tools and firmware files available in here: esp8266_xtcomutil.zip
+ connect gpio 0 pin to gnd before powering it up
Step 2: Configuration
i almost tried all other available utilities and only succeeded with this one. problem is it's seeing only first 6 comports, you have to open device manager by pressing win + pause and find your connected usb-serial device to change it's port number.
+ click port settings > advanced and change com port number to something between 3-6. first two one is your motherboard's native serial ports, you have to restart pc to assign number to them.
+ power up device and launch the xtcom_util.exe, select tools > config device and select your device's port number. 115200 baud is ok in most boards.
+ click open and connect, it will try sync for a while. usually takes 5-10 secs
Step 3: Write Firmware
+ click api test > flash image download and select ESP_8266_BIN0.92.bin from zip file. this is the very first stable firmware which comes default in most replica boards.
+ leave address offset as 0x00000 and click download, flashing process will take approx 2 minutes based on baud speed. you will see an unsecured SSID named ESP_A22A06 in your pc's wifi list if flashing is successful.
Step 4: Upgrade to Newer Version
Now we're restored the original firmware of esp8266 but it's functinality is very limited. it's okay for basic use but if you need more detailed functions like turning the dhcp on & off etc, you can try newer firmware file named ESP8266_AT25-SDK112-512k.bin from zip file, in my tests this one was most stable and newer version which works on blue boards.
if newer firmware fails, you can repeat same steps with stock firmware to restore default functionality.