Hello every one.. I have a 9,2 MacBook Pro, I had a problem lately with the computer performance, the problem is that the computer turns unresponsive from time to time, and needs a lot of time to do simple tasks, while playing video the video playback is very choppy, especially if playing a high resolution video (i.e. 720 px , 1080 px), I have tried reseting the SMC and PRAM but no success in resolving the problem, I checked the harddisk with disk utility but no errors were found, the S.M.A.R.T status is verified, everything seems to be ok! anyway, I read that reinstalling Mac OS X might solve the problem, but my internet connection is too slow to do that, and it fails in the middle of the way every time I try to, so I downloaded ubuntu and formatted the complete hard disk and installed it, to discover that the problem continue to persist, although the performance is a little bit better but the problem continue to exist, and it is very frustrating, when I play a 1080 p video from my external usb hard disk it plays smoothly, while it does not when playing from the built-in hard drive.. does this suggest that there is a problem with my hard disk and that I should go for a change? Any ideas??