|It could be either a few issues. One is that your computer is working on some stuff (good or bad stuff) and that is causing the slowdown. Get microsoft's security essentials and run it to look for malware or spyware.|
It could be that your hard drive is out of space or ram has good bad or some other setting is off or changed. Not easy to find but look at free space.
It could be that your videos at very big or some issue with VLC. Could try a portable version or VLC or just un-install and re-install it.
"The era of big government is over," said Clinton 1996