First, make sure that you can log on to your network with another device. If other devices are also unable to log on, then your problem is probably the network itself. If that is the case, try resetting your router or contacting your internet provider if that fails to work.
If the Kindle Voyage is the only device that cannot connect, there may be a problem with the WiFi antenna inside the device. Go back to the Kindle Voyage device page and click on the link to the WiFi antenna repair guide. Using the guide as a reference, open the device up and make sure that antenna is connected properly. If it is not, try re-connecting it and see if the problem is fixed. If the antenna is still not working, it will need to be replaced.