Cannot read Wireless network

Hi All,

I have a small wireless network at my workplace with around 20 Wi-Fi IBM
T40-series laptops. All the laptops have 3COM 3CRWE62092B wireless adapter in
it. Most of them are able to read the wireless network without any initial
configuration on the client machines except for loading the 3Com drivers.
Some 3 machines are not able to read the Wi-Fi signals/network. 40/64-bit WEP
key ecnryption is enabled on the access point. Following troubleshooting
steps are already done-
1. Downloaded the latest drivers from 3Com website and also from the CD
provided with the adapters, still no go.
2. Have tried wireless adapters from other good working laptops, no go.
3. Reinstalled the operating system, no go.
4. We have tried to configure the Wi-Fi adapter manually to the access point
by keying in the SSID and WEP key. It connect to the AP, signal strength is
good but cannot ping the default gateway.

What could be the reason for not pinging the default gateway? Any
inputs/troubleshooting steps greatly appreciated.

Thanks in advance.
Sridhar