Be certain that your wireless router or access point supports WDS. If it does not, you will not be able to establish a wireless connection with the Range Extender.
If MAC filtering is enabled in your wireless router or access point, make sure the WLAN MAC address of the Range Extender is entered into the accepted list so that it is not filtered out.
Be certain that you are using the same Network Name (SSID), channel, and security information as the settings for your existing wireless network.
You may be experiencing some wireless interference. Be certain that the Range Extender is set to the same channel as your wireless router or access point. If they are set to Auto, change the Range Extender, the wireless router or access point, and all the wireless clients to a specific channel. Make sure you set all these network devices to the same channel.
Try creating a connection to the wireless router or access point using an Ethernet cable. If you are able to establish a wired connection, go to the Web user Interface of the Range Extender and verify the wireless settings. These settings should all match those of the existing wireless network.