Games freezing: Kernel_data_Inpage_error

Computer Specs:

OS: Windows 7 Ultimate (x64)
Video Card: nVidia GeForce 550 TI
Proccessor: AMD Athlon II x3 450 @ 3200mhz
Memory: 4096mb (2x 2048 DDR3 SDRAM)
DirectX 11
Symptoms:
Computer runs fine outside of 3D applications. Inside, they're prone to freezing for 30 seconds to 1 minute, and after a while of playing, it bluescreens with a kernel_data_inpage_error, citing ntfs.sys as the culprit with a stop code of 0x0000007a.

This problem started with my girlfriend's computer after her video card died and she had to replace it with the 550 TI. She can play Civ 5 with no issues, but she encounters the problems in Portal 2 and Saints Row The Third. My first thought was the graphics card, since that's all that changed, but Civ 5 plays fine. I cleaned the video card drivers and reinstalled a fresh copy with no results. Then I tried rolling them back with still no improvement.

Then I turned off auto-restart on failure to catch the BSOD message and saw the errors. Thought it might be an HDD issue so I ran chkdsk /f as well as the Seagate utility itself. No issues.

Next I ran Memtest overnight with no errors reported, then I ran Video Memory Stress Test and it passed everything.

Lastly, I've just monitored system temps as she plays, and no spikes occur during the freeze. Cores hover around 35c but it seems GPU is climbing pretty high and hovering around 75c, but would high GPU temps cause an inpage error with ntfs.sys like that?

I'm at a loss, hoping someone can help out!


[EDIT:]

After running a game in windowed mode on her computer, it seems that while it's doing its freezing thing, you can effortlessly alt tab and the rest of the computer functions normally. So it's ONLY the 3D aspect that's seeming to have an issue!