Video And Audio Stutter In Games / Videos

the problem is stuttering. i get stutters in games, game movie scenes, videos, Internet videos, even as i type this to you know at times what i am typing doesn't appear, it stutters, then the words appear. in games, the stutter is probably every 10 seconds or so and makes games unbearable to play. with movies, the video will freeze but the audio will carry on, then once the stutter ends the video catches up and synchronizes with the audio. in firefox, like i mentioned earlier sometimes what i type doesn't appear for a few seconds, and also when i click on links it occasionally stutters. my laptop is an alienware mx15 which is less than 18 months old and 2months ago i wiped and reinstalled windows. things i have tried so far?

- updated graphics card driver which is a nvidea geforce gtx 420
- i did a disc defrag
- error checking of the hard drive (this got rid of the stuttering for about 10 mins whilst i was playing a game. however, when i go back to the properties on my c drive and look at this option again, there is the shield (2 blue quarters and 2 yellow quarters) usually this means an update, but nothing happens.