One persistent problem that some users have noted in OS X Lion is where Wi-Fi connections may not autoconnect when waking from sleep or when performing other tasks where the Wi-Fi connection is cut and needs to be re-established. Instead of locating a previously used network, the Wi-Fi connection will remain gray and require you to manually select a Wi-Fi network in order to connect.
If this problem happens to your system, you can try a few things to correct the problem:
New Location An easy step is to try creating a new network configuration in the Network system preferences. … Read more