FurMark GPU Stress Test: http://www.ozone3d.net/benchmarks/fur/ (uses OpenGL)

MSI Kombuster GPU Stress Test: http://www.geeks3d.com/20110407/download-msi-kombustor-2-0-2/ (uses DirectX and/or OpenGL)

Anytime your GPU is heavily stressed you can get "driver not responding" and outright BSODs (Blue Screen of Death) if there's an underlying problem with your hardware or software. Your GPU is suppose to be able to handle this amount of stress, and if it can't, it can indicate a few things:

• Bad hardware (busting/busted caps, etc.)
  
  
• Bad overclocking settings
  
  
• If not overclocked, may need to underclock a little (not all cards are the same quality)
  
  
• GPU fan is failing or just needs to be cleaned (overheating)
  
  
• GPU fan isn't spinning up to a high enough RPM, may need software fan control from RivaTuner, SpeedFan, Nvidia System Utility, etc.
  
  
• Failing / underpowered PSU (usually you'd only see "underpowered" if you upgraded your video card but not your PSU)

Additionally these should be considered even if you pass the stress tests:

• May need updated drivers, even Beta drivers, or may need drivers of a lower version
  
  
• May need a clean driver installation

It's important to do this so we can find out who has hardware that's working properly and still getting these errors.

That "driver not responding" bug is very interesting: It first happened to me while playing "Dead Island" and suddenly everyone blamed that game for causing it. But i can say - at least for my maschine - for 100% that this bug has nothing to do with a game, it only occures when Firefox is opened! The most time i get this message is when i am trying to write something in e.g. a forum, but also when i have a Firefox-window opened in the background while playing a game. Speaking for my maschine i can say that this bug has absolutly nothing to do with a game!

You left off failing/under powered PSU.

ya it's better to test with Prime95 or OCCT first
then if you pass those test with Furmark.

edit: make sure your pc will stay cool before playing around with these test

Yeah I had to set my fan to 100 for these tests, but passed furmark, though I have not had BSOD since ENB+1.3 patch

I compare tools like this to cranking up the volume to max on the stereo, leaving it there and if nothing explodes its all ok.
If after 2 weeks you start hearing a wierd humming noise and the thing suddenly goes *pop*, its probably not because of anything you did..