Ok do you see an a sword and shield icon on your main bar, what's happened by the sound of it is its appeared off screen so if you hover over the sword and shield icon till it shows the window above it, right click it and click move, then re click and drag onto your screen, if this doesn't work try to restart it. If that doesn't work let me know, im on the way to university so i cant really do much atm but i will try.