That's no problem Sandra. It seems that someone else was playing in his computer and changed some configuration.
He can make a taskbar appear by going to "Control Panel", then, "Taskbar and Menu", click on it, Tick "Lock taskbar" (which is the first option, and untick "Hide automatically the taskbar" (which is the second option). Also he can keep ticked the third option "keep taskbar over the other windows".
I hope the problem not more complicated than that.