If you have a habit of resizing the taskbar, sooner or later you are going to resize it to the disappearing point. You will not be able to grab it with the mouse. You may not even see it at all. But its there.
All is not lost. You can use keystrokes to get it back:
Hold down the Ctrl key and press the Esc key.
The Program menu should pop up.
Press the Esc key.
The Program menu should disappear.
Don't worry, there is a purpose to this madness: This makes the Taskbar active even though it may not visible.
Hold down the Alt key and press the Spacebar.
A menu will popup. Don't use the
Choose Size.
The mouse cursor should change to an arrow.
Don't click with the mouse.
Using your keypad arrows, press the up arrow.
The taskbar should move into visible space. When its back where you want it, click on the taskbar.