Hard reset TP-LINK TL-MR3420

Factory reset (Hard reset) Power ON the router. Locate the reset button (or hole) on the rear panel – it should be labeled WPS/RESET or just RESET. Press the button for about 5 seconds (but not for less than 5) – the SYS LED should start blinking faster. When this happens – release the button. Wait for the router to reboot



PS. For older versions of this model you might need a thin object to press into the button hole – try using a paperclip. The SYS LED is on the front panel and looks like a small gear icon.
Firmware Firmware link
Default username admin
Default password admin
Default IP address 192.168.0.1 or 192.168.1.1