I don't know if this will help but I upgraded to Yosemite Saturday night. No problems with wi-fi Sunday or Monday but got home today and no connection. Had to power off my computer, modem and router then re-start them in this order: cable modem, router, computer. Computer then asked for my apple id's for FaceTime, messages and iCloud. The wi-fi connection came back and has been working just fine throughout the house.