If you've formatted and re-installed the OS, make sure that you've installed all the correct and necessary drivers.
Also, note that if you manually disable the wireless device in Network Connections
, then the wireless button on the laptop will not work. The wireless device must be enabled in Network Connections in order for the wireless button on the laptop to be able to function.
Network Connections is located at Control Panel -> Network and Sharing Center -> Manage network connections (in the left-hand 'Task' pane) in Windows Vista and Control Panel -> Network Connections in Windows XP.