Macbook White Early 2008 freezes with 10.6.8 but works like a charm at all others previous version

Hi!

I have a Macbook White Early 2008 Core 2 Duo 2.4 GHZ, 4GB RAM (2 sticks of 2GB) and 500GB Hard Drive using Snow Leopard 10.6.8 and everything was fine till the day I had a problem with one of these memory sticks and suddenly the Macbook blocked/frozen. I turned of the computer, opened and cleaned the memory sticks and it became to work again. But, after a week or a little bit more the did happen again and I need to start a troubleshooting to found out what was the problem. In the first it was a little bit easy because the macbook was beep like it was a memory problem, so I tried to isolate them and apparently found the problem by removing the defective memory stick because the Macbook stop to beep and start to boot but fails in another point. I can see the white screen with the apple on the center and the spinning wheel, so the spinning wheel disappear and when it is about to show the login prompt it get stuck in a white scren and I can see on the screen a square with almost 2 inches the moves when a move the mouse pointer. I also tried to start on Safe Mode but the problem is exactly the same and when I chose the verbose mode I can see that it hangs on the message "PCI Configuration begins" message.

After these initial things I start to think that it was a software problem so, to avoid losing my data accidentally, I changed the hard to start a set of test.

1) I've got the Hardware Test DVD and did a normal and an extensive test. Everything went fine. Absolutely no problem.

2) I've decided to install the Leopard, the OS that originally came with it, and it installed with success the 10.5.2 version. I starting using for 2 days and did the update till the last version 10.5.8. Everything was OK but we don't have almost any compatible application to use with it. So it was pretty useless.

3) So I decided to install 10.6.0, that I bought on the release version and it also works like a charm. But the problem came back when I update the OS to 10.6.8. I tried 3 times the same process (install and update), the first one with automatically software update that popups up advising us about the update and the other two times by the downloading of the combo update (just to enforce that it was not a download problem).

4) Then, I install 10.6.0 again and try to make the update, version by version, to verify what version it starts to get the things messy. I was able to reach till the 10.6.7 version and when I tried to install 10.6.8 the problem appears.

Well, now I am running Snow Leopard 10.6.7, I found one 1GB memory stick so the macbook is equipped with 3GB RAM and everything is working ok. I already install the applications that I used and everything is found for more than one week.

I am a little bit afraid that the problem could get worse and start to fail even in other versions and I really don't understand what the problem is. I guess in 10.6.8 the graphic card or anything was updated and use more graphical resources, perhaps, and it is causing the problem because of a faulty hardware. But it is just a guess since the Hardware Test does not report any problem.

Thank you in advance for any help and direction.

Rafael, from Brazil