|Are you still able to connect to the router's management interface? If not, you may have to reset it to factory defaults before you can do anything.|
If you can't, and you reset, and you still can't, your router is probably toast and you'll need to replace it.
If you reset and you can connect to the management interface again, then do as Gretti suggested and ensure you have the most up-to-date firmware available for your device.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.