I have been having this problem for months and it is starting to drive me nuts. Sometimes - not all the time - when I open a Word document it will appear to open, but then disappear. But it does not REALLY disappear. It is there, but invisible. If I
swap windows with ALT-Tab you can see it is there, but you just can't get to it. The "missing" document is pictured on the left below with the other open document to the right.

The only way I have found to get to the document is to go to another Word document and select View, Arrange All. It then will allow me to click into the window and maximize it so I can edit as normal.
Again, this does not happen with every document I open, but only sometimes. And it does not always happen twice with the same document, so it is not document specific.
I am using Microsoft Office Home and Student 2013 with Windows 7. Most of my documents are saved in compatible mode, but I don't think they are the only ones that open this way.
This used to happen with my last computer (Sony VAIO) and I thought it was the computer's problem, but I now have a Lenovo ThinkPad and it still happens.
Any clue why this is happening and how to make it stop?