Hi Petal,
click the start button.
click control panel,
page should come up with a load of icons on,
click Taskbar and Start Menu.
you should be able to suss it out, with a little patience.
Good Luck.
It could just be that the bar has been resized to 'zero height'.
Try moving the cursor to the very bottom of the screen. If it turns to a double-headed arrow, it's resting on the top of the bar that you want. Hold the left mouse button down and drag it up slightly (to where the top of the bar should be).
Press the Windows key (between Ctrl & Alt) instead of the Start button which you can't access. Then go to All Programs > Accessories > System Tools > System Restore.
Petal, once you have it back, place your cursor at the bottom of the screen in the middle of the bar and right click on it. A pop up menu will appear. Left click on 'lock the taskbar'. That will stop it from moving/disappearing again.