On the Linksys Support Site, download the latest firmware and save it to your desired location.  For instructions, click here. Press the router's Reset button for exactly 10 seconds. Wait until the Ethernet and Wireless links will be powered ON.  For linksys wrt120n reset make sure that the Power LED is solidly lit. Access the web-based setup page of the router and update the firmware to the latest version. Power cycle the router then try to access the web-based setup page of the router again. Hold down the Reset button for exactly 10 seconds. Wait until the Ethernet and Wireless LEDs turn ON.   Make sure that the Power LED lights up solid. You should now be able to access the web-based setup page of your router.
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linksys ea7500 firmware