Windows 7 Screen and Audio Freezing Requiring Hard Reboot. Possible Graphics Card Issue

Windows 7 Screen and Audio Freezing Requiring Hard Reboot. Possible
Graphics Card Issue

Several months ago I was playing Minecraft and listening to the radio on
my Windows 7 desktop when the screen totally froze and the audio began
slurring, eventually descending into static then silence. I restarted my
computer and everything seemed fine. Several days later, I had the issue
again while playing Minecraft. At first it was by no means an annoyance
and rarely occurred when I played Minecraft. Fast forward to now, I
recently purchased a new game on Steam called Wargame: Airland Battle.
It's much more graphically intensive than Minecraft and rather than
experiencing this issue once every month or so, I've been having it occur
5 or 6 times in one day sometimes.
I don't know if the issue is getting worse or graphically intensive games
trigger the issue, and I genuinely don't know what to do.
The desktop I use was built by my brother and is several years old. It has
an Nvidia 8800 GTS graphics card. So far I've played with Airland Battle's
graphical settings with no effect. I've also done a clean install of the
graphics driver and done a cursory search of my desktop's innards. I have
also begun monitoring my GPU's temperature and have found that temperature
doesn't seem to affect the issue. I've had the freeze happen at 65 degrees
Celsius (which I'm told is a fine temperature for a GPU) and had it happen
in the mid seventies. I've also noted that the time spent gaming has no
effect on when the freeze occurs. Sometimes I can play for fifty minutes
with no freezing, sometimes just a few seconds, sometimes two hours. I
found a thread on the Nvidia forums where several other people with the
8800 GTS or similar cards reporting the exact same issue. However, those
folks along with myself have found no antidote. This whole issue is very
annoying and I hope that I will be able to find a solution quickly.
Here is a Dxdiag readout of the desktop in question:
https://www.dropbox.com/s/8iuv6lpcw58ihng/DxDiag.txt