Sajin
Sounds like windows updated your drivers for you. Re-install the older gpu drivers after cleaning the newer ones out with ddu. Disable windows updates while your at it too, to completely disable windows updates disable windows update under services.msc & taskschd.msc, also type into windows control panel "device installation settings", select "change device installation settings", change yes to no, windows updates should now be disabled. 

Situation update:
 
Disabled auto-updates to the best of my knowledge. Used DDU in Safe Mode to remove new drivers. Reinstalled old drivers. Rebooted computer.
 
Attempted to play Homeworld Remastered. Was able to get through two missions without problems, at high (though not highest) graphics settings. No crashes so far.
 
Attempted to recreate conditions of previous crash (the big starship explosion in Homeworld Remastered that previously triggered the crash). Big explosion occurred. No crash triggered.
 
Will have time for further tests tomorrow, and will report results. So far, so good.
 
Thanks again!
 
Evan

Update:

Played some Homeworld again. No crashes or problems.

Windows reinstalled a newer driver. I uninstalled it using DDU and reinstalled the older driver.

Is there a way to get Windows to stop updating the graphics drivers automatically? It seems that disabling Windows Update does not disable anything else. I can't find any option to disable only graphics driver updates.

Regardless, after reinstalling the old driver, I attempted to play Dragon Age: Inquisition. Attempted to reproduce the conditions of the first crash. Multiple battles occurred without issues. Gameplay was smoother than I have ever seen it.

Error message showed up saying that I had lost connection to the EA servers. This seems to happen from time to time. I closed the message, and ignored it. Further gameplay involved more battles, also without issues.

I was about to save the game. As soon as I clicked the "Save" button (or perhaps a fraction of a second beforehand?), my computer spontaneously rebooted. I performed a second (deliberate) reboot after this. To restore my Internet connection, I had to unplug and replug-in my wireless adapter.

The puzzling thing about this crash is that it occurred when the game was not displaying anything "fancy." It occurred seemingly at random.

Any ideas? Could this just be a fluke?

I will now test Warframe with the same driver and report the results.

Thanks again,

Evan

Sajin
I told you how to disable windows updates completely in post #30. I've done all those things and my system doesn't automatically update anything. Could be a psu issue if the computer shutoff like someone pulled the power plug and then plugged it back in and pressed the power button.

Sorry about my lack of clarity; I had followed the instructions you laid out, and it still auto updated the graphics driver. I was puzzled. Unless there was something I forgot to disable of course. :/

My PSU has passed two multimeter tests: one at idle, one while a game was being played. No voltage issues of any kind. Truly strange. Is it still possible for it to be a PSU issue?

I noticed something else as well: when I played Dragon Age, my GPU sounded much quieter. After the reboot, and while playing Warframe, it was louder, even though I didn't change any fan settings (and Warframe is a less demanding game). I don't know if that has anything to do with what's going on, but I thought I'd mention it just in case.

Warframe: played a less intense mission. No issues. Will try a more intense one and report results.

I know this must be incredibly frustrating for you; I really am grateful for your help.

Evan

Cool GTX

Sajin
I told you how to disable windows updates completely in post #30. I've done all those things and my system doesn't automatically update anything. Could be a psu issue if the computer shutoff like someone pulled the power plug and then plugged it back in and pressed the power button.

+1
 
"to reboot my PC spontaneously" = PSU fail or outlet power is not stable at the wall -- is my bet
 
Do your lights flicker in your house? 
 
Have you tried moving you PC to a different outlet, preferable on a different circuit ?
 
(Like, my PC only fails when someone runs the microwave or when I run my laser printer, both draw a lot of power would indicate a power issue at the wall plug)
 
 

Haven't had any light-flickering problems as far as I can remember.

I hadn't considered moving my PC to a different outlet before, but that is a good idea. Right now, it is plugged into a UPS, which is, in turn, plugged into a wall outlet. The UPS has several other devices plugged into it, although my PC is the only one that is currently on. I can attempt to test this possibly later in the week.

Even though my GPU temps are OK, is it still possible for it to be a heat issue? For instance, a faulty heat sensor that is too sensitive and is triggering a safety feature when it shouldn't be? Or could my temp readings be wrong? (I am going from memory on these, as I am not currently running any monitoring software while playing. Even on the Heaven benchmark with the highest settings, my temps did not read higher than 75C or 80C.)

Update: tried a more intense mission in Warframe. No issues whatsoever.

Evan

Sajin

Evan122688

Sajin
I told you how to disable windows updates completely in post #30. I've done all those things and my system doesn't automatically update anything. Could be a psu issue if the computer shutoff like someone pulled the power plug and then plugged it back in and pressed the power button.

Sorry about my lack of clarity; I had followed the instructions you laid out, and it still auto updated the graphics driver. I was puzzled. Unless there was something I forgot to disable of course. :/

My PSU has passed two multimeter tests: one at idle, one while a game was being played. No voltage issues of any kind. Truly strange. Is it still possible for it to be a PSU issue?

I noticed something else as well: when I played Dragon Age, my GPU sounded much quieter. After the reboot, and while playing Warframe, it was louder, even though I didn't change any fan settings (and Warframe is a less demanding game). I don't know if that has anything to do with what's going on, but I thought I'd mention it just in case.

Warframe: played a less intense mission. No issues. Will try a more intense one and report results.

I know this must be incredibly frustrating for you; I really am grateful for your help.

Evan

Your settings should look like this... http://i.imgur.com/E5SqkOI.png. Make sure to reboot your computer after changing the settings. If your psu passed two multimeter tests then your psu isn't at fault. Maybe your UPS caused the problem. If it happens again try running the system directly plugged into the wall.

Oh, I see now. It looks like I didn't use Task Scheduler properly. I fixed it and haven't had problems with auto updates since. Thanks again!

Update:

Have reinstalled old driver. All auto updates switched off.

Played through multiple missions of Homeworld and Warframe with no issues. Can test Dragon Age again as well. The old driver appears to have solved the issues.

Thanks again for your help. :)

Evan