MacBook Pro screen flickers and freezes after Snow Leopard/Safari 5 updates

Hi guys,

I have a silver 120GB 15-inch MacBook Pro from Summer 2007 with 3GB RAM and 25+GB free space which has recently begun to freeze irrecoverably. The first appearance of these symptoms seems to coincide with my installing the Snow Leopard 10.6.6 update via Software Update.

I'm not particularly well versed in computer technology, but will try to describe my problem as detailedly as possible.

What happens is this:

1. I start the computer as per usual, with only a couple of startup items. Everything's fine.
2. I start working. Use a lot of Safari 5 for browsing websites, often with some kind of Flash or "Flash-type" content such as banner ads, videos, even full Flash designs. I may also have programs such as QuickTime, VLC or an image editor open, if not necessarily "actively" doing anything. Everything's still fine - I'm able to both browse websites and watch videos as usual.
3. After a while of active working - say, 1-3 hours - I notice browsing websites gets a little choppy. Display features such as the file list view in Finder may or may not appear properly. The rotating wait cursor may or may not appear from time to time.
4. Immediately after symptom no. 3, the next time I start to watch a video, either via Safari 5 (say for example something on DailyMotion.com) or a file via QuickTime, something goes wrong.

Following no. 4, one of three things invariably happen:

5a) The video freezes and the entire screen flickers from black to the screen view very quickly two or three times, after which the computer or screen appears to freeze. The cursor still moves, but nothing reacts to it - open windows become completely unresponsive, nor does the top or any other menu react in any way to clicking. The "menu row" of application items, which normally appears when I move the cursor to the very bottom of the screen, doesn't appear. Restarting "blindly" by pressing the Off-button once and pressing R doesn't work. I'm forced to do a hard reboot, after which the computer is once again fine until the next two hours of active working. This usually happens ONLY when I try to watch a video in Full Screen-mode.

5b) I notice the video freezing only just in time, and am able to pause it and "esc" out of Full Screen-mode, and the computer remains operational. However, as soon as I again try to play video in Full Screen-mode, everything described in 5a. happens.

5c) The video stops playing, and the screen reverts momentarily to pale blue before switching to the login screen. I login again with my details, and everything appears to be fine again until the next two hours of active working. The computer "starts up" a lot faster than with a hard reboot. This usually happens ONLY when I've tried to watch a video in its original size, i.e. when not in Full Screen-mode.

This happens 1-4 times a day, and it appears to depend directly on how much work I've been doing on the computer. The less I use it in the course of a day, the longer it takes until the next time it freezes.

So, in a way, I'm able to replicate this problem. 95% of the time the screen has frozen while watching or starting to watch (usually already when starting to watch) video footage, but it has also frozen a couple of times just switching between e.g. Safari 5 and an image editor or browsing a website with a Flash banner ad or embedded video content (which however hasn't necessarily been playing); today, the screen froze when I tried to open a website made entirely with Flash.

Although it could be just a coincidence, I believe this issue first appeared when I updated Snow Leopard to 10.6.6 via Software Update alongside some other pending updates, including as far as I recall one for Safari 5. The update process appeared to have gone well at the time, though, and was not interrupted in any way. I have never had this specific problem with the computer/screen before, though.

I've read a couple of threads here regarding very similar issues with newer MBP models than mine, in which it has been suggested that the fault may lie in a malfunctioning NVIDIA GeForce graphics card. Now I've had that replaced already once because my screen went unexpectedly completely blank after a forced reboot 1-2 years ago (I don't remember exactly), but according to my System Profiler info the card still a GeForce 8600M GT. Can it be failing again?

I've also had some kind of a RAM card failure once. As far as I understood it, one of the RAM cards had fried and was preventing the computer from starting up. I replaced the bad 1GB card with a new 2GB one and the problem was resolved. Before the computer died, there were also other symptoms, but they were not similar to these.

I'm also doing the Apple Hardware Test tomorrow. Any other suggestions, though, than the graphics card?

*Could this have to do with Flash or Safari 5?* Just hear me out. Even though my computer has frozen from watching a video in just QuickTime, Safari 5 has always been open in the background at the same time, and more likely than not with websites with "Flash" content open. And come to think of it, before I performed the Snow Leopard and Safari 5 updates, I used to have daily problems viewing Flash video in Safari 5, the video content either suddenly showing up as "Plug-in Failure" or crashing the browser; I've had both Safari 5 and the Safari 5 Flash plug-in "quit unexpectedly" countless times in the past, almost daily. Sometimes the "Plug-in Failure" could be fixed just by refreshing the browser view; at other times, Safari 5 would stop showing Flash content altogether - Flash banner ads (such as Google ads), YouTube and other Flash videos, everything - until I quit and restarted Safari 5. BUT - since the day I updated everything via Software Update, I don't remember this happening; it never gets to "Plug-in Failure" now. Could it be worth trying to use e.g. just Firefox for a while or is there something (e.g. Adobe Flash) that I could try reinstall? Or am I just clutching at straws here?

Thanks for reading this long, long post!