PE13 Stops playback?

My students use Elements 13 in the editing lab, and we have been having multiple machines just stop playback while editing. Clicking on the play button, or the space-bar doesn't work. I have had to close the program and reopen it to make it work again.  The first couple of times I thought it was just a computer "glitch", but it is now happening on different computers more often. We are using Intel i7-2600 CPU @ 3.40GHz 3.39GHz 8 GB Ram running Windows 7 Professional. Using PE 13.1. I don't remember this being an issue before we did the upgrade to 13.1.

Thanks