OK, I see there has been a lot of support posts since I've been away, but not one to suggest buying a USB WIFI adapter. I think we are at the point where we got to admit defeat. This is one of those times, where Apple makes it unnecessarily difficult, by installing a WIFI unit inside that is so proprietary, it only works on MAC OS.
I just made a post about WIFI adapters, let me get you the link, and then you can pick from a list of WIFI adapters to try for your situation.
Hopefully you can get WIFI again provided by one of those devices.