How can i reset the dlink - D-Link DIR-600 Router

change the password with a new one (not the default), then change the ssid with a new one (not the default). then reconnect

Only you have the security code. Do a RESET of the D-Link, this will reset to default settings. Press and hold the RESET button until the D-Link resets , 30 sec. or so, Reconfigure the SSID and Security code. Take a look at this: http://support.dlink.com/emulators/wbr2310/index.htm

You need to log into the dlink router and look at the Wireless Security and you will see the password. To get into the router you will need the ip address of the router, the default user id and the password. You manual will give you this info if you do not know it.

Get online and got to www.google.com In the google search box type: "Dlink Support" (without the quotes and put your manufacturer name before Support). Look for downloads and drivers. Enter your model number and operating system when requested. Look for Manuals.

The IP address to put in your browser to get into the router is: 192.168.0.1

The default userid is: admin

There is not default password, so leave it blank.

the default dlink password is password or 1234
if that doesn't work then the password has been changed and you will need to reset the router to factory defaults. hold the reset button for 30 seconds while powered on.

It appears your brother has changed your wireless router settings.
You can reset the Dlink back to the default settings by -
Power off the Dlink and press and hold the RESET button on the back of the Dlink and the power on the Dlink. Hold the RESET button for 5 secs. until the LEDs flash at the same time.
Connect a LAN cable from the computer to the Dlink. Open a browser and enter the Dlink's configuration URL
http://192.168.0.1
Default login = admin
PW = blank (just press Enter)
You can now change the admin password and set up a new passphrase (ie encryption)
For details on how to secure your wireless from unauthorized access, please click on this link and follow my instructions :-
http://www.fixya.com/support/r3559128-wireless_router_security

In you dlink have a reset button, press that button up to 20 sec and then release that, your router will be reseted.

I haven't come across this problem before.
Try resetting the Dlink back to the factory defaults and configure the Dlink again.
Power off the Dlink for a couple of mins. then power it up and press the Reset button on the back of the Dlink for at leasr 5 secs. until the LEDs flash, then configure the Dlink again. If you use different SSID and encryption settings etc., then you need to configure the wireless card in the computers with these settings

Try to reset your Dlink, you can use as small pin to reset it. press the reset button for at least 1 minute and release, this will restart your Dlink to its original manufacturer settings.

If those light are all lit up and WLAN is OFF there's a big possibility that the device is getting bad, first thing to do here is to reset it , to reset the unit Press and hold the reset button for 30 seconds using a pen for about 30 seconds while the power is ON, then after that release the reset button and unplug the power of the router for 10 seconds and hopefully after that the lights should be back to normal but if not you may need to contact Dlink or get a new router instead...

Type 192.168.0.1 (you can type the router address if you have changed) and enter on browser's addressbar. Router's interface will appear.
Click on SETUP and Click on the WIRELESS SETTINGS at left side. on the page you will see the option of WIRELESS SECURITY by drop down menu you can choose the Security mode that you wish. here is the link for the emulator
http://support.dlink.com/emulators/wbr1310_revB/wireless.htm

Please post your question if you need further assistance
Good Luck