I've seen this kind of issue before. If the WiFi chip the modem stops working, then other devices will fail to connect to it or not find the WiFi at all. To make sure this is not an hardware issue, lets make sure the wireless is working by accessing router configuration window.
Connect the modem/router to your computer. Press Windows and R keys and this will bring Run. Type cmd and press enter. This will bring Command Prompt.
Then in Command Prompt, type the following the and press enter
This will bring some modem configuration details. Find and write down the Default Gateway address
Then open internet browser and go to that address, it is like 192.168.2.1, 192.168.1.1 etc
Then it will ask for Username and password. Find the username and password ***** here --> http://portforward.com/default_username_password/2wire.htm
Click on Wireless section and try changing the wireless name and password. Also change the wireless security (to WPA or WPA2 if you see that option) Also, if it is OFF, you will see an option to turn it on. Save and Apply settings. This will create a brand new WiFi network. Does your other devices recognize the WiFi network ?
Note : The above steps will not work if the WiFi chip of the modem is failed/failing. In that case, you may need to replace the modem itself. Please don't rate me bad or poor if you are not satisfied. You don't have to rate anything if you are not satisfied. You can close this page without rating and ignore rating requests. I will be happy to continue to help you until we figure this out.