Did you try doing a Hard Reset of the Router by unplugging the power cord and holding the reset button in for 30 seconds then plug it back in to see if it does anything?
If this should work, then you'll need to log back in and redo your configuration and be sure to set your Administrator Password (a strong one, not weak). Plus don't forget to set the password for the User access if there should be such an account as you don't want to leave this open either.
If the Router fails to respond to a hard reset, then it might have become bricked.
Possible causes could have been a power spike, a hacking attempt (doubtful), or one of the newer worms which attack vulnerable routers by flashing the firmware with a Botted firmware making your router part of a BotNet. The last could only have happened if you either left the router password at factory defaults or if you used a weak password (dictionary attack). A failed attempt at flashing the firmware with a Botted firmware would explain your Router being Bricked. (if it is bricked)
A good source of help is the
Linksysinfo.org Forums
They are not associated with Linksys or Cisco.