All the routers I have used always had a hole in the back for the reset button. You use a pen or pencil to push on the internal button.

Try pressing the reset button on the back for 1 min...make sure that the power light blinks while this is done... Keep holding the reset button and unplug the power cable... then release it after a few more seconds.. then plug it back in..

To reset the router
While the back of your router might look different, the reset button is usually clearly marked. To reset the router to the default password, insert something thin--like a pencil point--and depress the red button. Hold that for a few seconds. The password for your Linksys router should have reverted to its default.
Try accessing it from a machine that is plugged directly into it. The default address is usually http://192.168.1.1. When you gain access to the router then you can change the password to any word of your choice.
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After hitting the reset button for 30 seconds: try using the password adminxx (leave the username blank). I had the same problem, and this worked. If you need to find your network key or wireless network password, that'a a different problem. I can help there, too, if you need.