I'm assuming you forgot the wireless password key? If so, and if you remember your router's administration password you can log into your router by using a hard wired connection (ethernet), opening Internet Explorer and typing in 192.168.0.1. If I remember correctly with DLink routers, the username is admin while the password will either be blank or will have the password you put in.
If you've forgotten the administrative password as well, there is usually a reset button on the router (typically at the back of the router). Press this button (you may need a pin or the end of a paper clip to push in the button). This will reset the router to original conditions. Use the info I provided above to log into the router, then redo all the router connections (e.g. add the wireless passkey, change the SSID, change the administration password, etc).
Let us know if you have any other problems or questions. 
