Try doing a "hard reset/power cycling" with your router. It happened to me for a while, and i just got a new router because my old one was crap..
Hard Reset ("30 reset")
A hard reset sets the router back to the firmware's defaults, thus it will clear all the settings you have configured in the router. Here are some of the different ways that users are doing hard resets. Those methods will not unflash your router to the default firmware. They will reset to defaults such settings as IP address or password.
After a hard reset the router will take a few minutes to boot
Press and hold the button while the router is on, and keep holding it about 30 seconds. On different models you may see rapid flashing of an LED, or a red error or diagnostic LED. Wait for it to return to normal operation (typically power-LED on solid). Normal behaviour here is for it to not actually clear the nvram, although many people think of it and phrase it that way. What it is supposed to do is return all settings to factory state, or to say it another way, to firmware defaults. If you added new non-factory variables they should still be there after this type of reset. One way of tracking the status of what's happening while holding in the reset button is to leave a network cable plugged in to your computer and the router, then watch the screen on your computer. After the network has lost a connection for the second time, the router is usually reset back to firmware defaults.
If above method did not work at all it probably means resetbuttond is set to disabled.
Power Cycling
Some users refer to "power cycling" a router. Power cycling is simply rebooting the router, but usually by unplugging the router and then plugging the it back in. Some users claim to get different results by leaving the router "unplugged for a while".