I have a 15" Macbook Pro that I purchased 5 years ago. It is getting old, but I replaced both the ram and the harddrive about half a year ago. I have been having problems with the screen freezing for a while now. At first someone told me that my harddrive was probably causing the issue because it had been corrupted. I replaced it. The problem did not go away. Then I was told the problems I was having is software corruption, so I wiped the harddrive and reinstalled snow leopard OS. This did help for a while, but recently the problem has returned. My computer screen froze 3 times in an hour and I have static lines running horizontally across my screen. I have a screenshot example. Can you help me figure out what the problem is?