The users do witness a lot of problems when they try to reset Asus Router rt n66u, however hard resetting your Asus Router is not difficult.
 All you need to do is to turn the router off
 Then press and hold the WPS button
 And then turn on the router. Now. The power light is on
 Then you must keep holding the WPS button.
 Then, you should release the WPS button just after the power LED lights to start flashing
 Then flashing will stop, and the router will reboot automatically.

By following the above-stated steps, you can simply find out the ways to fix it.