|Maybe you've run into the problem I used to have. Until I built a new PC with a better processor, more RAM and a better video card, high resolution video used to give me a fit. Their higher bitrates are a heavy drain on the system.|
The first thing I would try is to run only one monitor and see if the movies play better. You could also try going to Task Manager to stop any unnecessary processes, thereby freeing up system resources. Another option, although fairly labor intensive, is to use a video editor to re-rip the videos that give you problems to a lower bitrate.
If you're not cynical, you're not paying attention