Random crashes during gaming

Hi all -

I'm at my wits end and hoping you all have some insights into my predicament. I have a 1 year old home built system with the following specs:

Motherboard: Gigabyte PA35-DS3L
CPU: Intel Core 2 Duo E84000
GPU: BFG 9600GT
RAM: G.Skill 8GB PC2 6400 (4 x 2GB)
Two Seagate SATA hard drives
A PC tuner card

System was running Vista x32 and was recently upgraded to Windows 7 64 (RC). Under both Vista and Windows 7, I get frequent but unpredictable crashes while gaming - primarily with older games like Civilization 4 and Medieval Total War. I thought a clean install would help which was part of my motivation for moving to Windows 7. Sometimes the game crashes right away - sometimes it'll run for 20-30 minutes before crashing. Temps for GPU get up to about 65 C under load - CPU temps never go about 53 C under load.

I don't think it's a windows error that's occurring. It's a hard crash to a black screen. The monitors flash like they have power but no PC signal. I have to hold down the power key to reset the computer. There's nothing obvious in the Windows Event Log - except for the messages about the computer not shutting down correctly. I can't find any .dmp files in the system. Which makes me think it's hardware, but...

Things I've tried:
Installed a new, more powerful PSU (went from 550W to 700W)
Re-applied thermal paste and reseated heatsink and fan
Run memtest (no issues)
Run disk error check (no issues)
Hard disk defrags once/week
Installed another cooling fan
Run both games in Windows XP SP3 compatability mode
Run both games with sound disabled

None of the above have worked. I have no idea what could be wrong - any help would be very much appreciated!

Thanks for the suggestion. Ran for 12 hours - no errors... any other thoughts?

Memtest ran to completion, if I recall correctly.

Other updates:
1) It's DEFINITELY hardware. I installed XP 32-bit on another partition and installed the games - same behavior
2) just in case it was the RAM, I removed half the sticks and rotated through - same behavior

So, I think I'm down to GPU or motherboard. Any suggestions on how to isolate it? In Medieval 2, for example, it runs huge battles just fine - only crashing on the AI turns - which you think would preclude the GPU but I can't tell anymore. I just don't get it...

Thanks for the help, Overclckr!

I don't have an overclocking tool as I'm not currently overclocking. Would those tools provide some insight into what's taking place under the hood?

Stability test ran for 1 hour - 414 tests completed successfully.

I also tried disabling the sound via device manager. Game still crashes.

One more data point - not sure if this will help - when it crashes, if there's sound playing the sound will keep playing in a short loop over and over again until I reboot.

Will do - I've got another set of RAM I can try tonight... my fingers are crossed

While on this topic, is there a certain pagefile setting I should be using in Windows 7? Back in the day it was all about setting a fixed size on the non-primary drive - I'm not up to speed on what the rules are these days.

Thanks for everything!

Cool - I'll try that.

As for the RAM: I didn't explain well - I actually have 4 x 2GB GSkill setup.

OK - zero progress - but I've tried a lot.

Swapped out the 4 x 2 Gskill for 2 x 1 GB and 2 x 500 MB ram that I had in my system before. Same behavior.

As for the voltage increase, it seemed like I might get a little longer before I crashed, but it wasn't much. And that's when it was cranked up to the flashing .7 + voltage. Could be my imagination, though - I have nothing scientific to back it up.

No events in the log. I can report that almost 100% of the time my USB mouse does not work when I get back into windows after one of these crashes - but I'm not sure that means anything other than the system did not shut down the right way.

Thanks for the help guys - I really appreciate it.

So, is it more likely to be my MB that's bad or my GPU? I'd love to experiment by my old PC doesn't have the right type of MB or GPU to swap.

UPDATE: Problem solved

It was my 9600 GT video card. I finally had enough and just went out to the store and bought a new card. Immediately the crashes disappeared (I bought a 9800 GT) after finding a thread that had referenced lots of issues with the 9600 GT OC cards. BFG released a second version of these cards which makes me think there were a bunch of problems.

What's interesting is that the computer never failed during any of the video card stress tests. Not sure how or why - but I'm happy to say I have resolution. It's RMA time.

Thanks for the help all!

Yea, unfortunately I needed to buy a card to even validate the issue having RMA'd a card with BFG before - I don't know anyone with a PCI-E card to borrow. I also couldn't afford to be without a PC for any length of time.

It was on sale @ BBY for $129

Probably should have done a bit more research before I headed out - I was massively frustrated after repeated crashes yesterday and saw the 1 GB 9800 GT (by BFG, of course - I really do appreciate the way they support their products)...

Oh well - I'm still happy (though slightly less so ) - I have a stable machine again.