|It could be a couple of things. Is this streaming video movies or downloads to your computer or already stored on your computer or just DVDs?|
Check for errors in the event viewer...
start > control panel > admin tools > event viewer and check all the different logs for any errors. research the errors found.
Check the computer for heating issues.
Check for bad memory....download memtest86 and run it for at least 12 hours or if any errors are found. errors are not acceptable and the ram will need to be replaced.
Make sure that your system is clean and free from any malware/spyware/viruses. And you might use the registry cleaner section from Ccleaner a Free temp files cleaner.
Change Is Good