*NOTE: Please ensure you have a computer hard-wired to the router, to ensure you can perform the necessary setup steps. Resetting the router will reset all settings, thus requiring you to reconfigure your router's SSID, encryption, etc.
On your router, there will be a small reset button -- it is often recessed into the router, so you may need to use a safety pin or pen in order to reach it. Press and hold the reset button for 30 seconds while the router is powered on.
Once the router resets, wait two minutes to ensure it completely reboots, and returns to normal operations. You should then be able to access it by entering 192.168.1.1 into the address bar of your preferred browser; can you login to the router using the default username/password?