Quicken, by any chance?

Quicken is especially prone to this problem. Here's what to do:

1. Get Quicken (or whatever program) to not be maximized. You can use
the Restore setting, click on the Maximize button or double-click the
title bar.

2. Right-click the Quicken icon on the task bar and then type "M" for
Move.

3. Use the arrow keys to move left or down. Once you start using the
arrow keys the mouse will work, and you can use the mouse to move the
window into view.

4. If that didn't work, the window is probably set to a 0x0 size.
Right click on the icon again, but this time, type "S" for Size. Use
the arrow keys, then the mouse as before to resize it.