When you say freezing is it locked up where you have to reboot or just that it slows down and then resumes? If you have to reboot then make sure your computer is
set for memory dumps and then see if maybe there are some DMP files you can include.
Sleep mode issues are common. You should check your ACPI BIOS settings. Check Advanced power options, maybe try High Performance. And also check Device Manager and maybe prevent some items from going to sleep.
First off, if you are streaming these videos from the web then delays are very common, especially if you live in an area with lower internet bandwidth; but even people with rocking throughput can find delays if the server supplying the stream is overloaded or limiting bandwidth.
Locally stored Videos still require a good deal of processing power so it is not unusual for them to slow down if your computer is also performing some of the many automatic updates including windows updates, AV updates, java updates, ccleaner, windows media center, etc in the background. What you may wish to do is monitor program & internet traffic with something like Process Explorer & TCPView to see if your computer is busy running other things. See our
Freeware DB for links to these apps
And you might also install malwarebytes and run it manually once a week or so as a secondary virus protection. Find links to it in the Freeware DB as well.