Wireless DHCP clients cannot obtain an IP address from the DHCP se

I had an update for windows xp 3 days ago. 2 days ago my laptop and PC (both
wireless connected) have the same problem:
They see the networks but they can not obtain an ip-address. Not from my own
network but neither from an unsecured network in my neighbourhood.

The PC has had this problem earlier (I did everything I could find on the
internet, the only thing that worked was winsockfix.exe). The laptop has
never had this problem.

Both computers have XP with new patches installed as soon as I saw them
(including off course SP2)

Anyone with an idea how to solve this.