From DD-WRT Wiki

Connect your modem to the router’s WAN Port. Plug in your modem’s Power adapter. Press and hold the router's reset button for 10-20 seconds for it to reset. Open a web browser, type 192.168.1.1 into the address bar and press the Enter key. Rear (RT-N12 D1) Label Description Reset Press this button for more than five seconds to restore the system to its factory default settings. Power Press this button to power on/off the wireless router. Insert the AC adapter into this port to connect your router to a power source. LAN1-LAN4 Connect RJ- Ethernet cables to these ports to establish. Here you can easily Reset Asus RT-N12HPB1 WiFi router for free. You can reset Asus router with the button or Web-Based Configuration Utility. You cannot update any security settings unless you know the username and password and access the router’s configuration utility.

This page is an attempt to clarify the different resets and reboots. You'll find other related and valuable information at Factory Defaults.

[edit] 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.

[edit] Hard Reset ('30/30/30 reset')

Holding down the reset-button while plugging in the router achieves a different goal than the thirty second reset. Here the bootloader is in charge, so getting it to clear the memory for you may have different results. Some platforms will completely empty the nvram and depend on another stage of the bootloader or firmware to repopulate it. On some less-supported hardware this may have unpleasant results, so use the following two reset methods cautiously.Note: On some routers, in particular a lot of Atheros based routers (and Asus), this may cause the router to go into recovery mode, instead of resetting the settings. It is often better to do a GUI reset, Admin tab, then factory defaults. Click apply and wait 5 min. The router is now reset and should ask for a password when you log into it at 192.168.1.1

To do a 'hard reset for anyone not knowing OP or otherwise, hold the reset button with the power on, for 30 seconds, then while continuing to hold the reset button, unplug the linksys router, continuing to hold the red button in the back for 30 seconds, and while still holding it in, plug in the power again and keep holding the reset button for an additional 30 seconds. This will wipe the nvram out. Keep in mind with hard resets the linksys routers can be touchy I had to do it three times till it fully cleared out the nvram on mine' I think this forum poster actually meant that it will reset back to firmware/factory defaults, but as stated above, it could have unpleasant results 'on some less-supported hardware'.

[edit] Power Cycling

Also called a Cold Boot, this means to remove power from the device for sufficient time to ensure all chip registers/voltages have cleared. Ten seconds off should suffice, but 30 is the norm, but if anomalies are encountered, leave the device without power longer. Ram has been known to be readable for minutes after a power off, and methods can be used to read said ram for hacking purposes. Chips have been known to maintain state for minutes as well.

Regardless, ram is supposed to be cleared on boot, yet there are various reasons why you can not be positive that this is the case. Design flaws, low cost design methodology, bugs in ram chips, can all result in ram or logic gates in chips, not being cleared on boot.

It should be noted that this will not clear the nvram nor reset the router back to factory/firmware defaults.

[edit] Clearing The nvram

See Erasing NVRAM in the Hard Reset wiki for command line details.
To 'clear, wipe, reset, or erase the nvram' commonly indicates 'to reset back to the firmware's defaults', although the two terms do not mean exactly the same thing. 'Factory Defaults' in DD-WRT really means 'firmware defaults' because it reverts to DD-WRT's defaults.

[edit] Login (password) after Reset

After a reset of DD-WRT, the firmware should ask for you to change the username and password. If it does not the reset was not successful.

Here you can find the default IP address and the username and password for the user interface of the ASUS RT-N12 D1 Wireless-N300 3-in-1 router. This site also contains information about the preconfigured Wi-Fi settings of the device. In the bottom part of this website, you will find a manual for accessing the user interface of this router and resetting its factory settings.

Login data for the user interface

Preconfigured Wi-Fi settings

Access to the user interface

Accessing the user interface is necessary when you want to change the router configuration. For the ASUS RT-N12 D1, you have to do the following steps for access:

1. Put router into operation
2. Connect the device via Wi-Fi* or a network cable with the router
3. Open web browser
4. Enter IP address in the address bar and confirm with ‘Enter’ key
5. Enter username and password in the open interface and confirm once more

* Make sure that your router’s Wi-Fi is activated.

Asus Rt N12 Setup Guide

Reset default settings

Resetting default settings is especially helpful when you have changed and forgotten the login data for the user interface. Please consider that not only will settings like IP address, username and password be set to factory settings, but all configurations you may have made will as well.

Execute hardware reset

To reset the ASUS RT-N12 D1 to its default settings, you have to do the following steps:

Asus Rt N12 Set Up

1. Put router into operation
2. Press Reset button for at least 6 seconds
3. Restart of the device is automatically executed
4. Default settings have been restored

Execute software reset

With the ASUS RT-N12 D1, you can restore the factory settings with the installed software. Log in to the user interface of the router with your access data and execute the steps that are described in the user handbook.

Reset Rt N12

After you have successfully executed the steps mentioned above, the configuration of the router will be reset to factory settings. If you want to log in to the user interface, you have to use the preset login data.