@Karen2121
Hi, you mean the extender was working fine before and suddenly stops working?
Please try to restart the extender and also your router, if the router works fine but extender still doesn't work, please let us know the LED status on the extender.
If the LED is red, which means no active connection, please try to reset the extender to factory defaults: While the extender is powered on, use a pin to press the RESET button, and the LED should turn off momentarily. Release the button and wait the extender to reboot to its factory default settings
Then set up the extender again:
Via Tether App: https://www.tp-link.com/support/faq/1373/
Via Web interface: https://www.tp-link.com/support/faq/930/