if it is your wireless router and you cannot remember the key you just need to reset it and it goes back to the default settings.
Depending on which router you have the default username will be whatever that brand uses. Google and see what your brand of router has set as the default password for the router. Now if you reset your router you will need to set up your password and such again.
So remember to set your password so your router is secure again after you reset it.
Reset is normally found on the back of the router, unplug it and take say a straightened paper clip and hold that little button in for about 15 seconds. It will just be a small opening on the back where you can fit the end of a paper clip in.
If it's not your router well hmm, can't answer that one.