please explain why all detected networks

Please give full information for the question that you have asked to get a meaningful answer and please fill up your System Specs.

I presume you have asked about a Wi-Fi Network. Even if the all the detected Networks come up checked, how does that affect your connection to the Net?

Normally one has to choose from one of the available Networks and press the Connect Button. After that you may be asked to enter the Security Code to get connected.