Hi Kandy_Man,
Since this also happened with Watch Dogs I believe it could be a system issue. I have found a few websites with possible solutions.
http://support.microsoft.com/kb/126962
Also, there seems to be an issue with a memory leak while playing a game in a different resolution than your desktop is set for in Windows 8.1. I would check that first, it seems to be the most simple solution. The site says that Microsoft is aware of the issue and are working on a patch. Before you run the Elemental Demo, go to Edit > Editor Preferences > Play > Play in Standalone Game and change the resolution to match what your monitor is set for. When you hit Play, make sure to hit Play in Standalone Game.
I hope this helps, TJ