Pls help immediately! - Can't find the window bar in the tool ba

I use computer a lot, but never had this problem.

When we open a program, such as Word, there should be a small window bar shown in the buttom toolbar, but now it doesn't. That means, even I open many windows such as Word, IE, Excel, and etc. They are just don't be shown at the buttom. Once I minimize it, it is gone because they are not shown at the buttom.

It is really killing me, and I can't work properly. Pls pls help!!!!!!!!!!!!