If your Cisco Linksys router is spinning on “waiting” after you enter your username and password there is a fairly easy fix but it does require a few steps. Reset to factory defaults then setup your router from scratch. This is usually caused by switching to the Cisco Cloud Connect firmware from the original Linksys style firmware.
Since you can’t get to the admin screen the only way is to use the physical reset button. On my EA4500 router it’s on the back of the router near the power plug and internet connection port. First unplug the Ethernet cable going to your modem (the yellow port labeled Internet). Get a paper clip or other pointy object and with the power connected to the router hold the reset button down until the Cisco logo on the front of the router goes dark and then begins to flash.
After the reboot the router will be un-configured and in a factory fresh state. It’s best to complete the setup with a computer attached to the router via an Ethernet cable and not wireless (because your previous wireless settings are gone).
Go to 192.168.1.1 in a web browser and follow the onscreen prompts. The default password you’ll need is “admin”. The initial setup does not give you a secure network so edit the wifi parameters to enable WPA2 Personal (or if you have a really good reason, some other setting). Then change the wireless password back to what you originally had it set to. If you pick a different password then all of your devices that connect via wifi will need to be reconfigured to use the new password.
Once the wifi setup is complete unplug the power from the router and from the cable or DSL modem. With both powered off plug the modem power back in and let it fully boot and connect to its network. Then plug the Ethernet cable back into the router’s yellow port and plug power back in and let it finish booting. It should now obtain an IP address from your internet service provider.
Update 1: In recent weeks the router has gone back to being inaccessible. I can use the Linksys app on my phone for most purposes because I don’t really feel like going through the hassle of doing a hard reset every couple weeks.
Update 2: There is finally a new firmware version for the E4200 that I use. It does overhaul the login feature but seems to introduce other UI bugs.