If you are asking about the wireless card in your Mac, it may have unfortunately failed...or it is not making a good electrical connection with the card socket.
In either case, this is job for the pros at the Apple store or repair shop.
If you are asking about something else....please provide more details.
My wi-fi icon in the menu bar is always dim (grey). I use my computer's wifi to connect to the internet on my iPhone. When I am able to connect to my computers internet via wifi on my mobile devices, the icon is still dim but has an arrow pointing up in the center of it.⬆ Everything I read about AirPort Extreme says the icon should be bold when the wifi is working. Could this be a problem with my AirPort card? I am using a '06 Mac mini with built-in AirPort Extreme 802.11g. If you or anyone has advise, it is greatly appreciated.