Can NOT connect to Wireless Network in certain order

I have 2 computers in wireless network. (WPA-PSK AES)

Computer A: Dell Inspiron laptop
Computer B: Desktop with USB wireless dongle.

Both Windows XP Professional SP3.
Buffalo AirStation WHR-G54S router.

Now, when Com A is connected to wireless first, then Com B won’t connect to the network.
It goes in loop of searching, connect, disconnect.

Now, only 1 PC will connect to wireless network at any given time.

No 2 wireless computers will connect at the same time.

Frustrating…

Can someone help?