Friendly Computers found this article useful and would like to share it with you.
One of the nicest features about the Windows 7 taskbar is the way it combines all of an application's windows into a single icon. Point to that icon, and up come thumbnails of the various Windows.
But Microsoft gave us the ability to change that display, so that every window shows up as its own taskbar icon.
It appears that you accidentally changed that setting.
To change it back, right-click a blank spot on the taskbar and select Properties. In the Taskbar buttons pull-down menu, select Always combine, hide labels.
You might want to try the other settings to see if you like them.
Source: http://www.pcworld.com/article/195865/separating_and_combining_windows_7_taskbar_icons.html
