Hi,
Welcome to the Microsoft Community.
Usually this issue is caused due to some settings related issues or due to not having updated drivers. I would like to know some information about this issue so that we could assist you further.
- What is the make and model number of the computer?
- Have you tried installing the latest wireless LAN drivers?
I would suggest you to try the following methods and check if it works for you.
Method 1:
Try the steps provided in the following Microsoft Help article and check if it helps.
Why can't I connect to a network?
http://windows.microsoft.com/en-us/windows/cant-connect-to-network#1TC=windows-7
Method 2:
Try the steps on the following Microsoft Help article and check if the issue persists.
If you are trying to upgrade to Windows 8.1 from Windows 7, then I would suggest you to try the steps in the following Microsoft Help article.
http://windows.microsoft.com/en-us/windows-8/upgrade-from-windows-7-tutorial
Please reply with the status of the issue so that we can help you better.