Make sure there isn't a hardware wireless switch on the side of the laptop that might be overriding your wifi key. If it is properly set and the key still doesn't work, you can go to your control panel->Network and Internet->Network and Sharing Center. In the left panel, choose "Change Adapter Settings" and find your wireless adapter. If it is disabled, right click on it and select "enable." If it is enabled, reply back saying so, and hopefully we can steer you in the right direction.
If this does not solve your problem, please post your PC specs in your reply, including the model number of the computer, as it will help myself and others with the troubleshooting process.