First of all I am not a Linux user. I work on Windows 7. So I will try to explain this in more simple way. Like Windows, there is a taskbar below in Mint. This is the gray bar which lies at the bottom of screen. When we minimize something like Firefox browser or any open document it lies on the task bar. When we click on it the window maximize back again. I do not know what happen suddenly everything disappeared. When I minimize something it goes to the lower right corner where the clock is. I can open that by pressing Atl + Tab, but I want the same thing restored. How I can bring the old stuff back.