This can be caused by an Internet service that's not fast enough to keep up. But since you gave no details about your service, that's about all I can say. It could also be caused by viruses and malware, so you should boot to Safe Mode and check for that. Have you run any kind of registry cleaner? That can also cause wierd and unpredictable problems that're hard to diagnose and fix.
I purchased the Gateway NE71B11u Notebook with windows 8 and having problems watching videos. I hook my laptop up to my TV with an HDMI cord to watch NBA basketball games and the video lags and stutters. It even does it on the laptop. It was fine in the beginning and all the sudden is doing it. Not sure why?