Problems with video length

I don’t know what have been happening to some of my mpg’s videos lately. I have several ones that looked like that had been edited and cuted. Files bigger than 150mb and that used to be longer than 30 minutes, now are just 5mins longer, at least it how WM shows in the status bar. It seems like the video had been corrupted, because i can search for scenes all over the video but they won’t play for more than a few minutes. And it happened to all my mpeg videos that have an aspect ratio of 1.34:1. I don’t if they used to have that aspect ratio before. Videos that are 4:3 are okay. This problem started when I replaced my cpu. Does anyone know if the changing the cpu can be the problem and if there’s something to do about it?