Looks like Mark already gave a good technical suggestion here. But maybe you were asking about the interpersonal aspect of this situation, in other words how do you handle a caller who's defensive and not very knowledgeable? I find it's almost always best to accept the user's point of view (no matter how unlikely it may seem) and go from there. At the very least, this helps to diffuse any hostility and puts you on the same side of the problem as the user. Once you've accomplished that, you can work to resolve the problem, and because the person sees you as being on their side they're much more likely to really listen to what you say. The best result is when that little "Aha!" light comes on and they understand what's happened, or even figure out their own solution. In any case, you've made a friend and probably reduced the number of future calls from that person too.

>I've spend about 14 hour per day in front of a computer and users calling at 9 PM don't bother me. I go or I coordinate them by the phone.
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>In this case, the user (a woman), has changed display resolution, from 800x600 to 640x480, and at first double click on My Documents, half of window was out of screen. (Top half). Now, please, put yourself in my place: the lady doesn't know how to manipulate a window with the keyboard, doesn't know how to go in Control Panel, and the little monitor icon from Systray is gone. I don't know where and how: the lady says: "Noooo! I didn't clicked anywhere! The computer is a stupid!"
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>If you were me, what did you do?