Lagging Video in Gaming PC ?

Hello Everyone! I'm new to the forums, and i've been having a very annoying problem. When i watch videos through Netflix, Youtube, i start lagging i can see the lips being slow with the audio. This only happens once again only when watching Netflix or Youtube or anything off the internet. When i first started watching it doesn't happen, but after like a minute it starts lagging and i have to move my mouse for it to stop lagging. When i watch something like from VLC Player or Media Player, there is no lag at all. I've tried cleaning the registry, cleaning the cookies, using different browsers, and even reinstalling windows 7 again and again. I don't know what's causing this problem, my internet is the best and it's great, my computer is a gaming computer also. Here are my computer stats:
The Computer is only 6 months old

Operating System: Windows 7
Processor: Intel Core i5-3570k
RAM: 8 GB
Motherboard: ASRock Z77 Extreme4
Graphics: NVIDIA GeForce GTX 660
Hard Drive: 112 GB Samsung SSD
(2) 1863 GB HHD

Please Help. Thanks!