Check by expanding C drive to see if you still have Windows old on your Computer, if so that can be deleted using Disk clean up. Those that have also downloaded the latest windows update version 1511 will also have a new Windows old that comes with it. It takes up 22 Gb of disk space and slows your computer down.
Wifi. Check in device manager for the driver details. If it is a Microsoft update. Run driver update and select let me choose which one. You should get a choice,Choose the one that goes with you Wirelaess card and not the Microsoft one.
Maybe do the same with your graphics driver or download the latest version from their sites.