Most of the times when this happens is because the antennas are disconnected.
Perhaps there is a problem with the TCP/IP stack. Try resetting it.
How to reset TCP/IP by using the NetShell utility
Besides that, there are other rare possibilities; I would make sure the wireless mode has not changed (default: 802.11a/b/g) in the adapter properties or that the only AP around you has the SSID hidden. Considering that these scenarios would be rare to find, I suggest using Intel® PROSet’s Manual Diagnostic Tool.
Intel® Wi-Fi Products — What are the Intel® PROSet/Wireless WiFi Connection Utility menu options?