Linksys Wireless Router :: Can't Reset Password On WRT54G

I have changed the router username/password in the past and either I can't remember it or its not accepting what I am entering, because the router logon will not go through. I have unplugged the router for 5 mins and then let it come back on and still cant get in, pressed the reset button down and let it come back up still nothing, and I have unplugged the cable modem and router for five mins and then plugged them both back up and I still can't get the router to reset to the default admin password. In the past it has worked before but now nothing I try will let me into the router interface to set up anything.