One of the biggest problems I come across, is when someone can't get their PC connected to their wireless home network. Yet, it seems to connect everywhere else but in their house.
Before I get the chance to look at it, I hear a long laundry list of things that were attempted to get the wireless connection working. Like re-typing the encryption password a thousand times, "rebooting the router first then my PC" (and a dozen other different ways), even moving the PC closer to the router.
But there are always two things missing in that list, if checked, may have saved hours of frustration and allowed more hours of surfing the web.