If for some reason a program window has wondered partially or completely off-screen, there are a few ways to get them back.

If you're running Windows 7 or newer, you can use the Windows key + an arrow key to align the window to a certain part of the screen the window is supposed to be on. This can also be used to reclaim your window, and get it back on the screen.

First, make sure the proper window or desktop app is activated by activating it on the task bar (click the corresponding button). Now, use either Windows + left arrow or Windows + right arrow to align the window to the left or right side of the screen, bringing it back entirely on the visible desktop. To give the window back it's original size, click and start to drag the title bar: this will resize the window back to before it was aligned, but it will remain on the visible screen area.

This works for all programs on Windows 7 and up. If you have an older version of Windows, there's one other way, but this only works with windows with a classic layout (i.e. they have a window menu, displayed as an icon on the left side of the title bar). The idea is to get to the window system menu, which is done by hitting Alt once, then press Left on your keyboard, then Down twice. While it may or may not be visible, this selects the Move command in the menu. Hit Enter: your mouse will go off-screen which in fact now points to the title bar. Hold down the left mouse button and start dragging the window back to the visible area of the screen before letting go of the mouse button.