The task bar may disappear due to a user resizing it, using multiple monitors and turning on autohide. All of these issues are something people can easily correct to restore their task bars.
If resizing is the issue, point the mouse at the area of the task bar, wait to see a double-headed arrow and then pull the border upward. With multiple monitors, users only see a task bar on one monitor, and this is normal. To turn off autohide, go to the Start button and go into the Control Panel area called Appearance and Personalization. People can find the Task Bar and Start Menu here and can then turn off autohide.