mac pro 2009 freezes and restarts while playing movies on VLC

i have a mac pro post 2009 and have noticed recently that while playing movies/tv etc on vlc it freezes and crashes and restarts. Is this a cpu or ram or graphics card thing overheating?? i have cleaned all the dust etc and otherwise is going fine. Could it be malware possibly?

any help gratefully am running latest osx and updates.

received thanks brent