Picture Viewing:computer Changing The Original Look Of Pictures

I have saved about 3000 photos in my computer under a folder called photos. But since some weeks, my computer is changing the original look of my pictures to very ugly views. I meant sometimes when I open my photo folders, suddenly some pictures are getting discoloured automatically. Sometimes the pictures are cutting to two pieces automatically. If the picture's background is green, sometimes it is changing to red, yellow or some other colour. But after this happened, I cannot get them back to it's original view at all. I don't know what's happening here. Already I have lost lot of my important photos because of this, and I even haven't saved them somewhere else. I already have deleted them from my camera too. Since I bought this computer, I am getting lot of problems in this. I don't know if it is because of VISTA or any other Hardware problem on this computer.