Sorry, but a few details are missing in your post so I'll just offer a common fix.
I get around computers pretty well but I'm a wireless networking newbie. And after plenty of research and phone calls to tech support, I'm stumped.
I just bought a new HP Pavilion DV9700T. I also bought the D-Link DIR-655 to connect to my five-year-old custom-built desktop PC. I have cable internet through a Motorola Surfboard modem. So I popped in the CD and ran the setup wizard. Everything seemed to go fine - the wizard detected all my connection, didn't even ask me any questions, and I was good to go. But I noticed right away that my internet connection was significantly slower. Usable, but about 80% slower than normal (I tested it).
So I removed the router from the equation and just hooked up the desktop PC to the cable modem. The internet speed was back to normal.
I reconnected the router and reset it. Updated the firmware. Read the manual, visited online support, and mess with every setting I could think of. Still, the connection was slow. (I should mention at this point that both the desktop PC and Pavilion had similarly slow speeds through the router.)
I confirmed with my cable company that it wasn't a setting on their end that needed adjusting. Then I called D-Link. On the online configuration tool, they had me go under the Setup tab, then to Manual Internet Connection Setup, then entering 126.96.36.199 in the Primary DNS Server box and 188.8.131.52 in the Secondary DNS Server box. (They tried to explain what this meant but I didn't catch it.)
This caused me to lose my internet connection entirely. After a couple more calls to D-Link in which they had me do little else besides cloning my PC's MAC address a couple of times and unplugging/replugging my modem and router, I still had no internet connection. So they told me to return the router for a new one. Then, just for the hell of it, I rebooted and got my internet connection back, although it is still slow.
So what can I do? Is it really defective, or is there something else to adjust? I have read where this router just doesn't work for some people, but I assumed that to mean it didn't work at all. Any advice is great as I would prefer not to send this back if at all possible.