These days it is fast and easy to make a separate partition and install an OS on it for testing though. I personally strongly reccomend this since it gets rid of so many possibilities when troubleshooting. Actually, when I set up a new drive I leave a 25GB partitionon it for this purpose. 
But yeah, you basically eliminate hardware failure as a possibility, and narrow it down to some interaction of installed software. Granted, its like going from finding a needle in a haystack to finding a needle in an average grocery bag full of straw.
It also pretty much always works. (unless you do have hardware failure)
There have been plenty of times over the years that I kept such a side-install simply to play the game that gave me trouble, then deleted the whole partition after finishing the game. Then 6-9 months later, when I reinstall the OS for GPs, the game will work on it. I never knew what the problem actually was, but in the end it didnt matter.
But yeah, you basically eliminate hardware failure as a possibility, and narrow it down to some interaction of installed software. Granted, its like going from finding a needle in a haystack to finding a needle in an average grocery bag full of straw.
It also pretty much always works. (unless you do have hardware failure)
There have been plenty of times over the years that I kept such a side-install simply to play the game that gave me trouble, then deleted the whole partition after finishing the game. Then 6-9 months later, when I reinstall the OS for GPs, the game will work on it. I never knew what the problem actually was, but in the end it didnt matter.