I have been using the same laptop for many years . Now I have a major recent problem in that I am having difficulty playing stored MP4 files . The playback is not good on windowed mode and un-watchable full screen . VLC , MPC worst , media player not great . One anomaly is that in windowed mode if I try and access the subtitle popup ,play almost stops . CPU usage is higher as well . MKV files , on pendrive and hard disk play with no problems at all . I have a large collection of MP4 on disk . Question is have I collected a bug / virus from somewhere ?