Guitar Hero 3: Legends of Rock is a music simulation game that was released in 2007. One notable feature of the game is the ability to play online against other players. The method to access online multiplayer is slightly different for the PC version of the game. This version of the game requires creating an online account through the game, as opposed to using an online account created through the console manufacturer.
Go to the main menu of Guitar Hero 3: Legends of Rock. This will appear automatically when you start the game. You can also reach it from any mode by pressing the "Back" button.
Select "Online" from the menu options. The account login menu will appear.
Select "Create New Account" from the login menu.
Enter a username, password and the license key on the back of the Guitar Hero 3 manual. The number on the back of the box is the serial number, not the license key. You must use the number from the manual to make an online account for the PC version of the game.
Press "OK" when finished. This will create your online account. Return to the main menu.
Select "Online" from the main menu to bring up the login menu again.
Select "Log-In" and enter your username and password when prompted. You are now connected online for Guitar Hero 3.
The license key on the Guitar Hero 3: Legends of Rock can only be used once to create an online account.