First, make sure your laptop is 'not' connected to the modem/router via an Ethernet cable and follow the steps:
1. Go to "Control Panel".
2. Next go to "Network and Internet" and then "Network and Sharing".
3. Now click on "Manage Wireless Networks".
4. On this screen, remove all wireless connections by "right clicking" on it and select "Remove network" from the drop down menu.
5. After doing this, close the oepn windows and reboot the computer.
6. Once the computer is fully reloaded, scan for the "Wi-Fi networks".
7. Click on the available network that you want to access and select "connect".
8. It takes a moment, but then you will be asked to give a password for your Wi-Fi connection. Type in the password and click the "connect" button.
It should now be connected.
NOTE: If this doesn't work, you may want to reset your modem/router, and then once it is fully loaded again, repeat the above steps.
If this doesn't work, test seeing if your laptop will connect via Ethernet. If so, then your WiFi card may be going. You can either look to replace it/have it replaced, or get an external (plugs in via USB) WiFi card.
Here is how I fixed wifi network not showing up. I was able to see and connect from my smartphone and another laptop but on another machine my WIFI network was not listed no matter what. I tried many things but this is what helped me. In Control Panel I found my wifi device -> Right click and then select Properties. Then click on Configure and changed the region to another value and applied the changes. (Windows 7). It worked like a charm. Some routers have possibility to change the region in router settings, but mine didn't have so this was the way I fixed it. I hope someone will find this helpful.