My Synchronous Scrolling works, as shown in this screen print:
Here a few ideas you might try to get your Synchronous Scrolling to work:
[1] Try clicking the Synchronous Scrolling button two times. Sometimes for me, as I experimented with Synchronous Scrolling, in my Word 2013 installation, it required me to click the Synchronous Scrolling button two times (I suppose that maybe the first click got the focus on the window, and the second click pressed the Synchronous Scrolling button).
[2] Check to see if your PC is set up for Dual Monitors, but you only have one monitor attached to your computer. In that case, I suppose it is possible for one of the two Word windows to be thrown over to your second monitor (which if this theory is correct, is not connected to your PC). To get to the settings for Dual Monitors:
If you have Windows 7, right-click on the desktop, and click on Screen Resolution. I am not sure how this is done in Windows 8 (maybe some other reader of this post could help with that, if need be).