Originally Posted by potter

First open Applications>Utilities>Network Utility

In Info, Select the network you are on from the drop list. Then there should be a button to renew your dhcp or something?? Try that and see if it works.

If not restart, and see if that works.

If that fails, then call Apple support. If you've never dealt with Apple support you'll be very pleased. One of the best support companies in the world. ;)