First off, try restarting the router by unplugging it, waiting 10 seconds, and plugging it back in. Do this before you play with anything else.
If that doesn't fix it, then make sure your laptop is hardwired into the router. Go to the command prompt (Start -> Run -> "CMD") and find your default gateway using the "IPCONFIG" command. Open up a web browser and then type in your default gateway into it's address bar (you should be expecting an IP address for the gateway). This will access your router's user interface.
Somewhere in the router UI is where you'll find settings for enabling wireless. Be careful not to mess with it too much or you might cause more problems than you are fixing. It's also possible that your router is password protected. If you don't know the login information for it, try Googling the router's model number and what the default username and password are.