One laptop won't connect to the network?

My sister's laptop will not connect to our home network, even though all of our other devices will. Or, more specifically, it will not connect to the internet. It works fine with a corded connection or when I use my phone as a wireless hotspot, but it still won't connect to our wireless home network. I've run the windows troubleshooter a couple of times and it keeps saying it has fixed the problem, but it never actually does. I've updated the adapter bios and still no avail, I've also cleaned the registry, updated the mobo bios, and am currently in the process of scanning for viruses. It has connected to the Wi-Fi in the past but my sister reports that it has stopped working the last week or so. It is a lenovo laptop around a year old running Windows 8.1. I swear, networking is my achilles heel. Any help you can give would be much appreciated!