Wireless LAN might have been Disabled. Check in network connections whether wireless LAN is enabled or not.
Open the Windows Control Panel. Control Panel can be found on the Windows Start Menu.
Click the "Network and Internet" or "Network Connections" option in Control Panel. (If necessary, first open the "Network and Internet Connections" icon in Control panel, then choose "Network Connections" from within that screen.) The Control Panel will refresh to show new options.
In Windows 7 or Windows Vista, click the "View network status and tasks" option from the Network and Internet window to open the Network and Sharing Center.
In Windows XP, the Network Connections window lists all Dial-up and LAN / High-Speed Internet connections installed. In the list of LAN / High Speed Internet connections, select the icon that corresponds to the network you wish to enable or disable.
In Windows 7 or Windows Vista, click the "Connect or disconnect" option shown to pop up a window displaying the current connection status. Use this window to first Disconnect from the active network and then immediately reconnect.
In Windows XP, right-click on the selected network connection. A pop-up menu appears. If the connection is currently enabled, the first option in this menu will be "Disable." Otherwise, the first menu option will be "Enable." Select this first menu option to alternately disable or enable the connection.
Close the Network Connections / Control Panel window when finished.
When a Windows network connection suddenly stops functioning, it's common to first disable and then re-enable it as a troubleshooting and repair technique.
Windows does not support Enable / Disable functionality for Dial-up network connections.
Starting with Windows XP Service Pack 2, a new Repair option is added for wireless LAN connections. Clicking the Repair button will automatically disable and re-enable the wireless connection.