Sounds to me like the other poster is saying.
Is that you have not installed the drivers after the new windows installation for both the Ethernet adapter and wirless network adapter for your laptop.
You should have a system restore, disk that came with the laptop, and you may of allso got a disk with all of the drivers for hardware devices of the laptop Mckennan.
I would check Or have a look for them depending on what brand name the laptop is.
If don`t have any of the two.
Then simply write down the brand of the laptop, then flip it over and you will find the laptops model number, write it down.
Then use another computer with a usb flash drive.
Search for the brand and model number of the laptop in a search query with google adding to the end of the search meta drivers.
Download the drivers off the support website for your laptop brand and model number.
You may have to extract the drivers from a compressed winzip archive first of all and then place the extracted files or folder created onto the usb flash drive.
Simply transfer the flash drive to the other computer, or laptop.
And run the driver installation files for the Ethernet adapter or Wi-Fi adapter of the laptop.