|Without that info you'll have to reset the unit to factory defaults (using the reset button) and then reconfigure it.|
With most D-Link's the default username is "admin" and the default password is either also "admin" (no quotes of course) or it's a blank password (as in, no password, just leave that blank). I'd try both variations of the default before resetting your router.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.