BSOD playing Half Life 2, sometimes right after start-up

Built a computer in August, it was running beautifully, but after some of my video card updates, it started giving me regular BSOD. I reinstalled windows, bought a new hard drive, reinstalled windows, and I still get BSOD.
I installed the newest BIOS from ASUS website which is right here

ASUSTeK Computer Inc. -Support- Drivers and Download P8Z68-V LX

I installed under BIOS the P8Z68-V LX BIOS 4003. Was slightly less buggy, and has only done a BSOD once since.

I apologize because this is my first computer, I don't understand all of the information I need to post in order for it to be useful. I really would appreciate any help in figuring out what the problem is. I've been trying to fix it by searching for drivers, updates, on forums for info since November (when it started to crash very frequently)

I uploaded the SF_23-12-2012.zip which just happened at about noon today. Usually the computer freezes up when I am playing Hitman: Absolution, but almost never when I'm playing Prototype 2. After updating my BIOS, Hitman doesn't BSOD, but just freezes. I've also been able to run Civilization 5 just fine, but that's what I was playing when I got the BSOD today.

Thank you so much for your time. My system specs are on my profile, but I can post them here if any of you need me to.

Code:

BugCheck 1A, {41790, fffffa8004391cd0, ffff, 0}

Probably caused by : ntkrnlmp.exe ( nt! ?? ::FNODOBFM::`string'+35054 )

Code:

Usual causes:  Device driver, memory, kernel

Follow these steps -

Test for any corrupted drivers, by running Driver Verifier for least 24 hours, stop the test if a BSOD occurs before this time frame. Driver Verifier will place stress on the drivers within your system, which will cause corrupted drivers to crash and hopefully be pinpointed.

• Driver Verifier - Enable and Disable

More Help and Information with Driver Verifier - Using Driver Verifier to identify issues with Drivers

Memory:

• RAM - Test with Memtest86+

Run Memtest86+ for least 7-8 passes, and preferably overnight as it can take a while to fully complete.

Test each RAM stick individually, if an error is found then move the same RAM stick into the next DIMM slot and test again, if errors are found for the same RAM stick in every available slot then you have a faulty RAM module. On the other hand, if no errors are found in the next slot or the other slots for the same RAM module, then you have a faulty DIMM slot.

Test each RAM stick and every motherboard DIMM slot available.

Thanks for the fast response. I did the Driver Verifier and then tried to run Hitman, game froze, no BSOD, then ran Half-Life 2 and got BSOD, attached SF zip folder. Will run Memtest86+ as well

And I was reading about the RAM thing, so I have two extra sticks of RAM. I swapped them out AND did the alternate DIMM slots, and Hitman would freeze still while loading my saved game. No BSOD yet, but something's still not right with the games not loading. On Assassin's Creed: Brotherhood, the game is stuck on the loading screen and won't load the actual game, the load screen where I'm Ezio just running around in a blank Animus. So I haven't been able to play the actual game yet, but have been able to start the loading screens.

Code:

BugCheck 1A, {403, fffff68000116040, dbb000014447886f, fffff68000028a1a}

Probably caused by : dxgmms1.sys ( dxgmms1!VIDMM_PROCESS_HEAP::Free+a2 )

Code:

Usual causes:  Device driver, memory, kernel

Code:

3: kd> .time
Debug session time: Sun Dec 23 22:52:51.266 2012 (UTC + 0:00)
System Uptime: 0 days 0:02:21.499

Place one RAM stick in at a time, and then run Memtest86+ for the specified amount of passes in my last post.