You've done the usual so it sounds like the usual failing wifi card. Yes it works in safe mode which proves little except repeating the same story I've heard too many times. We nod and listen and fit a wifi pc-card and it works again. Then the owner wants the internal wifi fixed. We've been there, done that and know to never do that as the owner will only come back next year when the internal has failed again.

Lesson learned.

One last idea. Change the wifi channel on the router. Be sure you are not hiding the SSID and the security is WPA.
Bob