I have a Dell D610 laptop running WinXP SP2, with 1470 Dual band WLAN adapter which connects to the internet through a Belkin F5D2370 Wireless router.
The router is configured with MAC filtering, WPA-PSK encryption and DHCP. The MACs of the WLAN and Internal NIC have been entered into the router.
When the laptop is docked and connected by wired LAN, the wireless has no problem getting an IP. .When I undock the laptop, the wireless loses its connection and I get the message warning me of "Limited connectivity". Sometimes I can get the connection back by disabling the radio, turning it back on and then reconnecting but this doesn't always work.
I have 2 other laptops, another Dell D610 and also an ACER, which exhibit the same problem. The signal strength is all cases is always Excellent.
There is another desktop PC which doesn't have this problem connecting on Wi-Fi.

Does anyone have advice on what I need to do to fix this problem?

Cheers,