If the adapter of a different manufacture, then configure the wireless settings on the adapter to connect to the gateway. The adapter needs to be configured for Infrastructure Mode using default for the SSID, no security. Eliminate distance as a possible factor by moving into the same room as the gateway. After you gain wireless connectivity, you can customize your wireless settings (SSID, security, channel, etc).
Also from Dlink
Make sure the following wireless settings are the same on the AP and wireless adapter:
* SSID (SSIDs are case sensitive)
* WEP settings (make sure the encryption levels and keys match)
* Network Mode is the same (Infrastructure or Ad Hoc)
If you still cannot get a wireless connection try disabling all security settings(WEP, IP address blocking, MAC address filtering, and enable the Broadcast SSID). Change the SSID to ANY on all devices. If you still cannot get a wireless connection try moving the units closer together.
hope that helps.