The are several things because of which your computer might not detect the wireless signal. First, make sure that the signal isn't blocked by random items, such as walls, doors and so on. The closer your computer is to the source, the stronger the signal will be. There are some devices that can interfere with your network signal, such as microwaves. Remove them from your computer's area. Also, check the functionality of the wireless adapter driver. Go to the developer's webpage and download and install its latest version. A router adapter has a pre-defined limit of supported computers. You can check the limit number of your router on the manufacturer's website. The router or access point might be overloaded by the computers that are currently connected to your router and might be incapable of responding to new requests. Try disconnecting a few devices to see if your system is recognized. Also, the access to the router might be restricted by the administrator and you will have to remove this protection manually.