I am using Microsoft Word 2010 in Windows 7.

I have this same problem occasionally and I have noticed that it is triggered when I accidentally hold a key down a little to long, and type several of the same characters in a row, for example if by mistake I type: "Executiveeeee Summary" then the cursor shoots uncontrollably to the top of the document and the screen freezes.

The solution I have discovered is that, if I press control+alt+delete and open the task manager, then click on "end task" Word prompts me before it actually does close the Word program. At that prompt, I can cancel the request and it unfreezes Word and sends me back to the document. This has worked for me repeatedly.