You won't be able to figure out the password unless you have written it down somewhere. The best thing to do would be to press and hold the reset button on the back of the wireless router and/or modem to remove the security on it. You will need a small paperclip or fine-tipped pen in order to do this. Then allow about a minute for the devices to reset. After that, all of the computers should be able to connect to the network without any security authentication. The only problem is that all your neighbors with be able to do the same.
In order to setup the password again, you need to know what model of router you have and connect to the IP address of your router using internet explorer or another web browser. Most can be accessed by the following:
192.168.0.1
The default security that will popup with ask for a user name and password, which are typically admin/admin or admin/password. You can then go through the menus to add a password under wireless settings. Hopefully this helps and good luck.
