Game hard crashes, screen goes blank, audio loops forcing shutdown

[shiphorns]

I've purchased LC:GoL and Underworld through steam, and I'm having the same problem with both games: they start up normally, but 2-7 minutes into playing I get a hard crash where my video card just stops outputting any video, and the machine is left playing a 4-second (or thereabouts) loop of the game's background music indefinitely. I can't ctrl-alt-del out of it, the machine needs to be powered down. Problem is identical with both games.

My system configuration is:
- Mac Pro 2008, 8-core 2.8GHz Xeon
- Windows 7 Professional x64
- 6GB Physical RAM
- ATI HD 3870 512MB video card

Nothing is overclocked or modified, it's pretty much a stock machine with a video card upgrade (the 3870 card being the proper Mac/PC retail version, not some sketchy flashed eBay deal). My system is completely stable with the exception of these two games.

I'd love to know what's going on, in order to get the games playable, but I can't seem to find any type of logs to give me the first clue about the crash. FWIW, I had the non-Steam retail version of Underworld and played it 2 years ago on this same hardware without issues, the only difference being I was running XP Professional SP2 back then. This leads me to suspect Win 7 x64, but it could just as easily be any number of things--new video drivers, new DirectX, etc. I need to figure out how to identify the cause of the crashes.

Here's what I tried based on forum feedback from users with similar issues:
- I disabled all anti-virus software and rebooted
- I turned off Steam's cloud sync
- I verified the Steam game cache for both games
- I ran Catalyst Control Center and disabled all advanced video settings, including "overdrive"
- I uninstalled Realtek High Definition Audio drivers and ran the game audio through my USB M-Audio Audiophile box.

Note: I'm also using an Xbox controller with the MS Win7 drivers (not emulator), if that matters.

[shiphorns]

I've done some more testing, by running MSI Afterburner, and I've concluded that the GPU usage of this game is causing my graphics card to overheat. Here is the data, you can tell me if this seems reasonable.

I cleaned the graphics card heat sinks and fans with a spray can duster. I then downloaded MSI Afterburner and use the monitoring facility. I played GoL for 2 minutes. After 45 seconds, the graphics card fan was solidly running at 100%, and over the 2 minutes of gameplay the GPU went from 56C at idle to 96C. Even with the card's fan going 100%, the temperature graph was still rising when I shut the game down. I have no doubt that it would run away and overheat.

In comparison, playing Minecraft or LoL or other games that are light on GPU usage barely raise the temp of the card (Minecraft full screen got it to 70C, but stablized there and was kept in control by the fan which never exceeded 66% speed).

So.. is this as simple as a defective and/or poorly designed card with insufficient ability to cool itself?