I've pressed something by mistake, I leaned on the keyboard on the bit that has control/shift/capslock - and my toolbar at the bottom of the screen has vanished (the bar that has Start on the left and the icons for printer etc on the left).
I think F11 does this it's press for on, press again for off kind of thing - but some keyboards have the F11 in blue so you have to press the blue alt key and f11 at the same time.