Graphics/directX related crashes

Hello,
I'm new to this forum and looking for some help w/ odd crashes....

I've had an (MSI) MS-1719/GX700 laptop for over 3.5 years, and it's been working great till about a couple of months ago when my Hitachi SATA HD (80gb) crashed on me (mechanical/read-write heads failure). I replaced it w/ a Seagate SATA 500gb, Reinstalled winXP SP3 and the various drivers up to date/software I had on the original HD....

Everything seemed ok, till I started having crashes in various situations/ with various software, where the screen would simple blank out, nd the fan would start winding up, and nothing...no keyboard/mouse or any input seemed to get things back to normal.
The computer was/is still on when this happens, but it's non-responsive. if I click the mouse/keys too much a loud beep/s would come from it, but that was it....the various LED lights are still on.
The only way to get back to normal is rebooting the machine. When rebooting, windows doesnt even seem to have registered that anything was wrong, since it didnt give me a choice to reboot in safemode or normally (at least not winXP it does later in win7).

the following are the situations when this happen everytime:

1) - When using Firefox (tested versions 4/5/6) at what it seemed like random sites/pages and even when clicking on the "Add-ons" link under the "Tools" menu...crashes as mentioned above. After some testing/research I realized that the only way to get firefox to work, was to turn off its "hardware acceleration"...then it would work just fine.

2) This issue then came up while playing Grand Theft Auto 4....I would be playing it for a while all ok, and oddly it seemed that only when it rained inside the game (which seemed to put more strain on the vidcard anyway) then it could blank-out/crash as above, and again the only solution was to reboot.

3) I have an nvidia geforce 8600GT. When going to its control panel, the very top option under "3d settings" called "adjust image settings with preview", as it loads the nvidia spinning 3d log, it would, again crash as mentioned above.

4) in windows 7 64bit (home premium edition), the "Windows Experience Index" rating...as it was processing, the progress bar was saying "Direct3d 9 Batch Assessment" or something similar...it crashes again.

here is the following troubleshooting I did so far:

I spend some time uninstalling/reinstalling, even rolling back to previous version drivers for my geforce 8600 GT...even using DriverSweeper in safe mode to make sure I cleaned up remains before installing new drivers.....actually rolling back to an older driver seemed to make things a bit more stable.....meaning I could play in some of the areas/conditions in GTA4 that would crash before w/ the newest drivers...but I would still get crashes similar to above, both w/ GTA4 and firefox, just not as many/frequent....

I also decided to use a number of utilities to test my hardware for corruption/overheating:

- memtest86 for RAM - no errors/issues
- prime95 for CPU (torture test) - no errors/issues
- furmark/OCCT for GPU/vidcard - no errors/issues
- OCCT for ram/CPU/GPU combos - no errors/issues
- OCCT for vidcard memory - no errors/issues....
- SeaTools for the HD - all tests were a pass...
- even tested directX w/ dxDiag.....no issues there either.
- clean boot w/out startup items (with the MS services still on)......the problem/crash is still there...
- ran windows diskErrorCheck utility with both "Automaticly fix file systems errors" and "Scan for an attempt recovery of bad sectors"
- ran System File Checker - after verifying it said "Windows Resource Protection did not find any integrity violations"

I also considered overheating...I could not find specific max/safety temps for my CPU/vidcard/mobo....but using CPUiD HW Monitor and OCCT, I could tell that even under full stress my vid card wouldnt go above 75/80C temps (normal around 50), and my CPU on full load (for hours at the time) wouldnt go above 100C...normal around 37. the mobo under full stress would go around 104C.....none of these seemed to me (and also from doing some research) like above normal when under full stress.

I've also been scanning for malaware/virus w/ Norton Internet Security (my default AV/firewall setup), malaware-bites,super-anti spyware, spybot and Hitman Pro...nothing found.

At this point I was at a loss as to what was going on, so I decided to move on to Windows 7 64bit a couple of days ago.

Tried Firefox and at first it worked great!...no crashes/issues...so I was encouraged!

However the GTA 4 game crash still occurs as mentioned above, as well as everytime I try to run the "Windows Experience Index" rating, as mentione above.

So here I am...very frustrated and at a total loss as to what's going on. Any direction/help would be MUCH appreciated!

here's a link to my detailed specs/hardware status as it is now..

thanks in advance,
paul

Graphics/directX related crashes - help needed!