I spent 2 days figuring out sudden loss of wifi connection with my Toshiba laptop and windows 8.1.
I tried almost every recommended fix I could find on the internet. finally found one that worked and
it was easy! just uninstall wifi network driver(mine was realtek) and go to Toshiba service station on your computer ,the latest updated driver will be listed there, download it , when it finishes installing
restart your computer if it doesn't automatically do it. luckily for me I could get on the internet by the
Ethernet cable!! I know some people can't do either , recommend uninstalling both internet drivers
and downloading latest drivers recommended by your computers manufacturer ie. Toshiba, lenovo
etc. Goodluck all! p.s. Toshiba recommended manually uninstalling several components BEFORE
downloading windows 8.1 from the windows store, just go to their support sites for the list.