I'm guessing you're talking about your WiFi transmitter, yes? That you have forgotten the password and can't connect to it?
If my assumption's correct, here's what you do.
On almost all WiFi transmitters is a reset button that requires a thin piece of wire to press. With the WiFi utility application on your computer open, and ready to go, press the button with a piece of wire, or a pen tip, and wait to see the WiFi unit pop up in the window of the application. This will allow you to rename the WiFi transmitter and reset the password.
You will then have to go to all your other devices to reset the passwords on them.
Update: If you're talking about the internet router that provides internet service to your house, there should be a password sticker somewhere on the unit itself. If it isn't there, you will have to call the company to have a technician come out and reset it.